You have come to the right place; many people here will have a lot to say about what you are asking. Most will have more experience than me.
I've been doing what you want to do for about 6 months now.
I have a Praise Team that meets in my Garage to practice and we have started recording a few things. I've got 4 Audix Dynamics, an AT Condenser, an external set of Pre-Amps and Compressors, and I went the PC route.
I would think that if someone is computer literate, they should lean towards the PC route.
The portability part can be fixed with a rack-mount PC case in a standard 19" portable rack that also houses any pre-amps, compressors, effects, and patch bays you get. I have a rack case that I'm planning on building up.
The biggest plus for PC for me was its cost to ability ratio and ability to upgrade. I had most of the parts lying around. Many things can be downloaded free or try before you buy type demos. The beginner level software is not very expensive. You can upgrade software as it and you improve. You can add capabilities as your studio grows. You can use the PC to burn CD's and email MP3s.
I'm getting off your questions... Here is my opinion to some things:
Mic and Pre:
Many people are going to give you many answers. Some might even think no pre is good until you spend $2000 and no mic is good unless it's maid in Germany and cost $800+. My opinion, you have to find the mic and pre combo that work for you and the other singer's voice and the sound you like. At this point, you probably don't know where to start. Do you have a place you can demo these type of things. For me, I don't think it's wise for me to buy a very expensive mic and pre set until I know what I want. So, I decided to get entry-level stuff that I can use for a while until I start to learn the basics of what things like proximity effect, tube coloration, presence hype, and compression sound like. So this is what I did for vocals, I bought what was described as a fairly neutral mic (AT3035 $150) because other mics that have "character" require knowing what type of character you like and what type you don’t. I bought a 2-channel pre (BlueTube $100) used. It's not the best but I am having a good time learning with it. I can send my mic and my bass guitar to it at the same time and it does a great job for me. I also got
the Presonus Blue Max Compressor for 2 reasons. It matches my BlueTube and is made to share a rack space with it. Also, it has presets that say things like Vocal 1, Vocal 2, Fretted, etc. that where designed by the manufacturer that I can use until I learn how to do my own settings. My 1 step up in all this will be a new mic (after I learn my voice and what I want), a new pre on the level of the RNP or the new studio project pre (I mention these because they are <$500 (SP is <$200) and have a lot of people talking). And I will probably get a RNC (compressor) because it is said to be the best compressor for the $ and if I get the RNP it would mate up like my BlueTube and Blue Max do. Bottom line is that Mic and Pre are mostly personal preference and you can't know until you try, so I'd say get in cheep at first while you develop your taste and know what you want and then you can invest more in future gear that will be "keepers" when you know what you want to keep.
I got the Roland Studio Pac ($599). It is a digital mixer board / 8 channel in and out PC Interface Card / Recording Software Package. It was a good bet for me because it's like a mix between an all-in-one, a DAW, and a stand-alone mixer. I can use just the mixer part without even turning on the PC for practices. The 8 channels of simultaneous recording is enough for me. The most I have used is 5 at a time for a drum kit and it worked great even on a relatively old (400Mhz AMD) PC.
One thing that I would be interested to hear (read) comments on is acoustics. You mentioned recording you amps. I know that it standard in studios but they have rums that acoustically work for this. I prefer to run my Bass direct or use my effect box to act as the "amp" sound. I know that there are POD type boxes for guitars also and I've read good comments about them. They would eliminate acoustics, mic selection, mic placement, preamp, etc. from the equation. I know that I have been experimenting with using a bathroom to record vocals because the garage is too big a space. That became obvious as soon as I moved to the condenser mic (picks up more of the room noise).
If you do mic the guitars, think about Shure SM57s. I don't own any so take my word at that, but if you don't already know this mic, write it down. Hundreds of people on this board have them and will tell you why they are the most useful $75 studio mic. I seem to read that at least once or twice a week. I will have some soon. So far my set of Audix OM-2s are filling the bill until I have extra cash to burn or see a price that I can't resist for a set of SM57s.
Phantom Power: Some mics need them (Condenser) some don't (Dynamic). Some things can be damaged if phantom power is on while they are plugged in. This is important because often low cost mixers provide phantom power in an all or none fashion. That means either all the mic inputs have phantom power on or none of them have it. So, if you are going to be running a mix of dynamic and condensers at the same time (like when micing drums or some multi-mic acoustic guitar setups), you need separate pre-amps, phantom-blocker type circuits, or stand-alone phantom power supplies. Both my Roland mixer and
my BlueTube ether provide Phantom Power to both mic inputs or none.
Compressor:
First, difference between a pre and a compressor: A microphone produces a tiny weenie little signal, the pre-amp amplifies it to line-level signal. When the signal is tiny weenie, it is very susceptible to noise because it is so small that even the smallest interference is comparable in size. So, it's best to pre-amplify the sound as close to the mic as possible. There are many more aspects involved in mic preamps but this gives you the basic idea.
The compressor is quite different form a pre and a little more difficult to explain. Basically it takes a signal that has quiet and loud parts and makes the loud parts a little quieter. Have you ever watched a movie at night while others where sleeping? You got the quiet parts that you have to turn up to hear and the loud parts you have to turn down to avoid waking the house. The difference between the quiet and loud parts is the (amplitude) Dynamics of the audio track. A Dynamic Compressor brings the quiet and loud part's closer together. This is useful for sources that get quieter and louder as they perform, like voices. You usually want the voices to have relatively the same volume in comparison to the rest of the song so that you can still hear it when the singer is singing the 'airy' parts and it's not obnoxious when he/she is belting it out or hits that resonate note for their voice. It makes it easier to record when it's a little bit compressed because you usually want to record a track with as much signal as possible without clipping. A limiter is also used for this. It's like a compressor but it dramatically stops the volume from going over a set level. Your compressor settings can dramatically effect how the recording sounds. That's why I got one with the presets and not as much flexibility, while I learn.
Signal Chain:
First thing the mic goes too is the Mic Preamp as I alluded to above. When recording you don't want much else but it could go like this if you wanted all of this: Mic-Pre-Noise Gate-EQ-Compressor (or compress then eq)-DeEsser (takes the exaggerated [ess] sounds out-(mixer-interface-recorder).
You can get 'channel strips that include all the stuff from the mic pre to the de-esser. I bought the Antaries Vocal Producer ($417) and took it back because I decided that that money was better spent on just a Mic and a Preamp for me at this point of the game. There are cheaper channel strips (Behringer Ultra-Voice $125) that could be used to learn on. I've heard some say that piece is great and others say that it is noisy. But, at that price it's a cheep way to learn about Mic-Pre, Tube Saturation, Compression, Enhancement, EQ, and De-Essing in one box. It's probably not the best at any of these things but until you know where you want to spend the bid bucks, it might be an option. The other way to learn about this stuff is how I'm doing it. I got a cheep Mic Preamp and I'm learning the rest in software. Most of the recording software comes with soft versions of all this stuff that you can tweak on while you learn what it does. Most of it even has presets to get you to a starting point.
My signal Chain:
Mic-Preamp-compressor-Roland VS3100pro (Analog to Digital happens in here)-Roland PCI Card in PC-PC Hard Drive.
I plug the Bass into the Preamp and record it the same way.
Guitar-Effects Box-Roland VS3100Pro-Ect.
Mic: I'm one of the least experienced here so I'll just try and share what I've learned in my reading and talking to those who know more. Rule Number One: Mics are a very personal preference. Rule Number Two: SM57 is the most versatile, cheep, studio mic.
I use my dynamic mics on each drum and the condenser as an overhead. I don't get pro results. But I don't get pro results on anything yet. I think it would be unreasonable to expect that and based on your questions, you’re in the same place as me. I'm in learning mode. I read that the SM57 is the standard Snare Drum Mic. There are also mics just for kick drums. There are large diaphragm Condenser mics that can do voice and Kick Drums (B.L.U.E. Baby Bottle) and there are small diaphragm Condensers that I read to be more suitable to overhead use than large (more sensitive to transients).
As far as the part about a lot to buy with a DAW... If you compare All In One, DAW, and Discrete Units (one item for each function) the DAW fares nicely. If you are only interested in what the all-in-one provides and nothing else, that would be the one stop solution. But (big but), you will likely want other things like pre-amps, compression, effects, the list goes on forever. When it comes to a DAW, you 'could' go a simple as having one unit that is the mic-pre and interface then all the compressors, gates, effects, etc can be software based. Any of the full feature software packages include most of this stuff. Great thing is that if you have say one software compressor, as long as your PC is capable, you can have separate compressors running on as many channels as you need at the same time. If you where hardware compressing, you would need one for every channel.
Personally, I think you could get by with an 8 channel DAW system (lets you learn inside the software where you should feel comfortable), a nice but entry level mic pre for recording vocals (<$200), a vocal mic that both singers like, maybe a simple compressor (one like mine for ease or RMC to grow into), and enough mics to capture your drum set with at least one that can be used on a guitar cab. My mixer only has 2 XLR type plugs for mics but it has basic mic-pres on 8 inputs. With the right cables, I can hook up as many as 8 mics for things like drums and do an okay job without separate preamps and compressors for each channel (that can come later).
There is many ways to spend more money than anyone has. If you keep simple for now but allow a path for upgrade, you'll be recording soon but not replacing the whole shebang in 6 months. That is where I see the PC solution working out for a PC savvy person such as you.
Hope I've helped.
God Bless You Too,
neener, neener 
