You'll need to do some of your own research as you define your needs and refine how to prioritize spending your money.
Off the top of my head, and in no way designed to be a complete answer:
1) You probably won't need a mixer- if you're working in Pro Tools you'll be mixing in the box (meaning in the computer) and you'll probably benefit more from spending your cash on...
2) The best preamps and mic(s) you can afford. At your budget that probably means using the pres on your interface and getting a decent mic. I don't know what mics are currently in favor for rap.
3) You'll probably go with a PC - so plan on keeping that sucker OFF the internet. If you're going to go with Pro Tools head over to duc.digideisgn.com and look around for computer recommendations there. If I recall, there are ongoing and detailed discussions of what hardware works best for pro tools.
4) At that budget you are talking about Pro Tools LE. (sigh) This locks you into a relatively low quality set of choices for your audio interface. This is a trade-off of sorts: do you shell out for a 003 and forego the outboard preamps or get a lower quality mBox and hope that better pres will give you a better sound. At your budget you probably don't have much choice.
In reality, hardly anyone you're likely to work with is going to hear a huge difference anyway. You may not either until you've logged a lot of hours using the stuff. I haven't kept up on all the new mBox variants out there these days - but in general rap requires no more than 2 channels so the firewire interfaces won't give you any advantage. I might go with the Mbox 2 that lets you use SPDIF inputs just because you can upgrade your convertors and pres later without also having to upgrade your interface.
5) Studio foam. Good. You're thinking on the right track- a little investment in making the space sound better can have a huge impact on your sound quality. Its also an easy way to spend a lot of money... read everything you can before spending anything here. Seriously. A little sound treatment goes a long way IF its done right. A lot of sound treatment can go a little way if its done wrong.
That's all I have at the moment. Hopefully that's at least slightly interesting reading if not actually helpful.
-C
