Well, the AT drum mics should all be dynamics (as far as I know), so you don't need phantom power yet. If you want to plug them directly into an 880 then you are correct, the inputs are 1/4, not XLR. When I first got my 880, I was using the XLR to 1/4 in transformers (still do sometimes when I just want a simple recording of a jam).
If you shop around there are be some other brands that make HD recorders with build in preamps that will take an XLR cables, but I'm not sure if any are in your pricerange.
I have a cheap Behringer mixer, and I can take the output from each mic (before EX and effects) out 1/4 in, so I was doing that for a while before I had any preamps.
As for guitar, the drum mics are not ideal. You might want to surf around the Mic forum a bit. A lot of people like the Oktava 012s or the Marshall 603s on guitar. I haven't used either of them yet. I think my good ole SM57 sounds decent on guitar and sax (I play a little alto too), but I'm still a newbie to recording!
As for transferring to the computer the 880 really can only do it 2 tracks at a time (although, you can have a project with however many tracks and send them all in to editing software 2 at a time). That is the main reason I am in the process of switching to a computer-based setup, to eliminate that extra step. I just got a Tascam 428 on ebay for $310. It's a bit more complicated to setup, but I think I'm going to like it a lot better in the long run.