You would probably be better off with an Apogee Duet. I know several local musicians who have recorded an entire record using their duet, macbook, and logic.
I would borrow the mics instead of buying them or it could get very expensive. If you must buy, think about Cascade Fathead II Ribbons or Studio Projects C4's. They are both iin the $300 range for a pair and both will work well on acoustic guitar. You can vary the distance from the guitar and each other to achieve different type of results for flatpicking, fingerstyle, or strumming.
Someone you know has a nice pair of mics they would let you use for that reason. If you know a taper, he might even come over and record it for you to gain the experience.
Many musicians I know will set themselves up with a simple two channel signal chain for the purpose of putting down demos and doing overdubs on other projects.
Preamp/AD combos such as the API A2D or Grace m201 would make good front end signal chains to get into your system.
The Apogee Duet works pretty well from what I've heard too, decent preamps and excellent converters and gets you directly into your DAW.
Goodluck, PHil