I feel like there are some semantic misunderstandings in this thread, and since I've just spent the last three months researching this EXACT problem (use interfaces w/ pre's OR use interfaces w/o pre's in conjunction with a console [mixer] as a pre-amp sending signals into the interface), I think I can clear things up easily.
But before I get into that, let me give the OP (original poster) some advice on this forum: you have gotten responses from three of the most knowledgeable guys on this site: Jimmys69, RAMI, and bouldersoundguy. These dudes REALLY know their shit, so I would heed any advice they offer.
Ok, now to the semantic confusion: first, the OP says he's gonna use a Mac but then says he's buying a recording PC called a "Mac Mini." Well, is it a PC or a Mac? It can't be both. (I Googled "mac mini" and the first result was an external hard drive; do NOT record directly to an external drive. BAD idea. Use the external as a backup or for playback but always use the internal hard disk when tracking.) If yer gonna rawk ProTools, then get a Mac; ProTools coding is just not meant to run on Windows OS. But that's the most expensive route.
Personally, I find ProTools to be extremely overrated and somewhat inflexible in terms of some specific routing options; there are a TON of other great DAWs out there that will run really well on a PC. And, you can build yer own PC for a fraction of the cost of a Mac: I built a new desktop recording PC last year for about $850, and a year later it's STILL faster & more powerful than any Mac currently available. You'd have to spend $3500-$4000 to get a Mac that matches my PC's power & speed. I would also HIGHLY recommend utilizing Solid-State hard drives as opposed to the traditional spin-based drives; they're slightly more expensive but since there are no moving parts, they generate almost zero heat, and the lack of moving parts means their failure rate is almost non-existent. (If you would like any advice on building yer own PC, feel free to PM me.)
Onto more semantic tomfoolery: the OP is confusing interface terminology. When an interface says it has "X number of inputs," it means that it can send "X" number of individual tracks into your computer at once; the number of outputs refers to the number of individual tracks you can send OUT of the interface at once, most likely during playback.
In terms of FireWire vs. USB, I *completely* disagree with the statement that FireWire is only for Macs; the motherboard I installed in my new PC last year has FireWire built into it. However, FireWire *IS* on its way out, and USB 2.0 will serve most home recording functions just fine; if not, USB 3.0 definitely will. And that's not even mentioning the new protocol hitting the market, Thunderbolt.
In most home recording applications, the number of inputs on an interface is more important than the number of outputs (excluding stereo/monitoring outputs), as most home recording enthusiasts will process everything ITB (in-the-box), meaning they will use plug-ins and other software-based effects and the software mixer as opposed to outboard effects & consoles; sending a signal out of yer DAW into an outboard effects unit or console is probably the most common use of outputs on an interface where home recording is concerned.
In my home studio, I use the outputs on my interfaces most commonly for re-amping a signal (Google that term if yer not familiar with it) or for sending mix stems (another term to Google) to an outboard summing mixer.
All that being said, I find a combination of both methods mentioned above (either straight-in to an interface with mic pre's or into a mixer first and then out individually into an interface) is the best route for home recording. I've got a vintage Tascam M320-B console I refurbished recently, and I've got the line outs from each channel on the Tascam routed to a patch bay, where I then typically route the signal from the console into the line level inputs on one of my M-Audio ProFire 2626s (I have two chained together). If I don't need or want the console in the signal chain, then I go straight into either the ProFire or will use an outboard mic pre first and then go out of that into the interface.
So, depending on what kind of recordings you plan to create and the methods you'd like to use as well as the level of quality you wish to output, there are quite a lot of options for you. Personally, I'd take the advice of most of the contributors and stay away from cheap, low-quality mixers like the Mackie ProFX; they're great for basic live sound but in terms of recording, they're a no-no, in my opinion. You'll get much better results if you eschew the mixer all together and get a couple decent interfaces, pre-amps, and of course, MICS!
Your options for interfaces are hugely variant, but you should easily be able to reach just about any amount of inputs at a ton of different price points. You could go the route I've gone and stick with mid-priced interfaces like the ProFire 2626 and the Tascam US1800 (Behringer, Focusrite, and MOTU all offer similarly-priced options); or you could go a bit higher and look into the MOTU 896 products; or you can go a bit higher with certain RME products; or lastly, you can get REALLY high-end and go with Apogee Symphony products, the Antelope Orion line, or the UAD Apollo units, which are incredible if you plan to use a lot of high-intensity plug-ins, but you pay for the power & quality.
Hope that helps!