I would start by looking for an 8 channel preamp with ADAT lightpipe to add 8 more channels of simultaneous recording capability to your setup. You mentioned the PreSonus one...you might also want to look at the M-Audio Octane and find out what others have to say about that. I think it runs a couple hundred bucks less, but it might not be as good in quality either. If you're going to be tracking multiple musicians at once you need to consider setting up cue mixes and monitoring. It could be a solution as simple as a Behringer headphone amp, or taking it a step further and getting a "control room" unit like the Presonus Central Station. You'll also need headphones for the musicians...you can get cheap phones from AKG, Sennheiser, and Sony, or contact Harvey Gerst about some of his MoreMe phones. And don't forget about monitors...you'll want a decent pair so that you can hear what you've got going on when you track and mix.
If I was in your situation, I would A) save up about $500 more, or commit to that much more on the credit card payment; B) get
a Presonus Central Station; C) get the best set of powered monitors I could find in the $500 ballpark; D) get a Behringer Powerplay headphone amp with three pairs of cheap headphones and one good set (Beyer, Sony, AKG, A-T, etc); E) get a good power conditioner to handle everything; and F) spend the remaining money on the best 8 channel preamp with ADAT Lightpipe that I could find. Lets see:
Central Station $500
Monitor budget $500
Headphone amp $100
3 pairs MoreMe $100
1 pair Sony cans $100
Power Cond. $100-$150
Assuming an 8% sales tax, allthis would come in at just over $1500. Take the rest and find the best preamp you can. If need be, ditch the headphone amp for now because the Presonus has two headphone outputs and I think the 002R has one as well. Don't be afraid to test the used market, you might find some bargains that save you a couple bucks. Also, don't forget to factor in cabling costs...they add up quick.
After you have all that, start looking at improving your mic selection, and maybe adding in some good plug-in suites.