I want everything to be plugged in and ready when I want to do something, and be able to accomplish my tasks quickly. I plan on doing some programmed instruments like keyboard and drums, and would like to add a decent little electronic Ringo kit eventually so I can actually get back into playing drums some more. Any keyboards, however, would certainly be programmed. Can't play keys very well but I can program like a son of a gun.
For a DAW I would suggest Reaper. The program itself takes up very little hard drive compared to others. It is only $60, plus free updates as they come, and compatible with PC or Mac. (I run PC) As I'm not a real tech kinda guy, I found it pretty easy to learn. Tons of tutorial vids on their site, as well as tips/tricks/shortcuts on youtube.
For interface, I would go with a 4 channel that has midi in/out. That way, if you eventually get an e-kit for drums, (and/or keys), you can midi in with that and still have 4 inputs for you and three others. If budget is tight, Behringer might be a way to go. A friend recently picked up a Behringer U-Phoria UMC404 for $150 from
Sweetwater. He likes it a lot. It has phantom power also, which is nice if you use condenser mics.
For drums, I picked up an Alisis Nitro mesh kit ($380) and use Toontrack EZdrummer 2 for sounds (as well as programming ). Quick note on e-kits. Advise I got from a couple drummer friends that actually use electronic kits. Get mesh heads, and what they call a kick tower. A mesh head that uses an actual kick pedal as opposed to the lesser expensive button trigger bass drum. They told me main difference in lesser expensive and expensive mesh head kits is the module. Kits like Roland have a big library of great sounding kits, where as kits like Alisis, like the one I bought,has a much less expansive library, of which, only 2 or 3 usable kits. (IMO). But I was not concerned with the limited internal sounds, as I bought it to trigger sounds from EZD2.
As far as keys, sounds like you have a pretty good handle on programming, so you can paint (write) in midi, and there is a huge selection of vst's ranging from free to ridiculously priced. Just keep in mind, if you're doing a live session with anything being recorded through midi, you need a vst for sounds. But you probably knew that.
All and all, Reaper @ $60 (or any inexpensive/free DAW), and a 4 ch. interface @ $150 - $300, you would have a pretty rockin' home studio.