Hey, first off, welcome to ts.com! I would definitely put the most money that you can towards mics, some options that I like in the few hundered dollar range:
AKG C1000- kind of a newbie standard, can be had for about 200 bucks for a pair
Superlux SMK-H8K- I started w/ these mics and I really like them over the C1000s, come with a bunch of accessorys, pair $130ish if I remember correctly
Octava MC012A- becoming popular for taping, 200 for a pair
You will need pantom power to power thoes:
Art Phantom III is a cheap phantom source for 50 bucks
Samson mixpad 4- this would be a little more versitile because it is also a pre, so you can adjust gain ect.. under 100 used is common
MD is a lossy format, in that it compresses the music, while dat does not. Dat records to a digital tape, not to an internal harddrive. Another advantage to dat is that you can run 1 tape up to 3 hours, while 1 md is only 80 minutes long. I would say go with dat if you can.
Yes we run 2 mics to get a stereo sound, see:
http://www.dpamicrophones.com/eng_pub/ go to the "Microphone University" and click on stereo configurations. DIN, NOS, ORTF, XY are all commonly run in the field.
If you need any more help let me know, I gave you some low cost options because I dont know how much your looking to spend, if you have more money to spend, let me know and I can give you some better gear suggestions. have fun, +T!!!