So you essentially want to do the Nelaelu's One Person Band?
You could also go with Avid's
Digi Eleven Rack which comes with Pro Tools LE 8. I know they're on 9 now, but still it's a four input interface and PT 8.0.4 cs2 works just fine. PT 9 is not interface dependent. Eleven Rack eliminates the need to mic a guitar amp and your sound will be consistent. $900 for an interface, amp modeler, and DAW? Not a bad price for the bundle.
Depending upon your environment (I'm assuming home studio room) where you might have to deal with outside noises, you might also want to look at a Fishman Aura Sixteen pedal for your acoustic/electric guitar -- this unit uses mic modeling for specific guitars, so if yours is one of those guitars you're golden. It adds space between the guitar and interface. Space that doesn't exist if you go in directly. Hence it can eliminate the need for miking the acoustic. $200
Keyboard? This isn't going to be cheap. You could go with
a M-Audio ProKeys 88 which is pretty inexpensive. I'd look at one that at least has a speaker and some similar sounds to any virtual instrument you'll be using. Why? Virtual instruments have latency. You can set it pretty low but on some things I've found myself consistently 1/32 note early depending upon the tempo since I tend to compensate my keystroke for the latency. You may already have something and if you do you're golden. I use an Alesis QS8 and
a Yamaha MSR100 monitor for this and as a midi controller. Also M-Audio Axiom series goes to 61 keys and has transport control onboard so you don't have to run back and forth. Another is the M-Audio Oxygen 88 (new) which has graded hammer action and transport control. I don't know how good it is but it isn't expensive. These run around $600. I'd also check the used market here. You can save some money.
You're not going to get out of a good vocal mic. I have both a dynamic SM beta58a and a condenser mic. My condenser mic is no longer made. That will run you about $400 to $700.
The Neumann TLM 102 looks like a good one for $700, or you could go Shure KSM32 for around $500. Personally, I'm a Shure girl.
Then you'll need drum software. I've been using XLN Audio's Addictive Drums for a couple years now. I've got several of the Ad Paks, and I find them quite nice sounding. $229 for the entry level kits and beats. You can add Midi Paks for like $12 ea, and the full Ad Paks which include kits for around $60 ea. Yes they have a Metal midi pak.
Monitors?
Samson Resolv A8 which are available at Sweetwater.com. These are a best bang for the buck. $400 pr.
Let's see this comes to $2829 without cables. So assuming the $3000 isn't the absolute top end grab some Mogami Golds as many as you need, although seriously I'm using less expensive stuff with good results -- you'll find on the cables the price difference on the length is more in the connectors. Personally, I'd buy a spool of bulk shielded instrument cable and a bunch of solderless connectors and make my own. It'll be cheaper in the long run.
Now remember, you have just stepped into a money pit. Next you'll want virtual instruments like Reason 5, or Komplete 7.
I haven't treated my room since I'm still not settled on the arrangement. Being able to go DI with my guitars, and my vox tracks haven't been harmed, and use of VIs, has reduced the immediate need for treating. Besides, new eyeglasses are taking priority over room treatment.
I'd really look at Sweetwater.com's web site for a lot of info. They've got great customer support, and have tutorials on various products online, and free lifetime support on any software you buy from them.