#1
So I'm planning to buy some gear in order to record some guitars/bass/vocals, and here is the list:

http://pro-audio.musiciansfriend.com/product/M-Audio-Fast-Track-MKII-USB-Audio-Interface?sku=703669

http://pro-audio.musiciansfriend.com/product/Shure-SM58-Microphone?sku=270101

And I have Cubase 5 on my computer. I'm also planning to record with my Peavey 6505+ Combo.

Would this be everything? Or would I need more equipment?
Gear:
Ibanez GRG170DX
Peavey 6505+ Combo (60w)
Roland Cube 20w
Ibanez TS-9
Boss Chorus Ensemble CE-5
#2
Maybe instead of the 58, try the 57. Works really nicely on guitar amps, and vocals are pretty good too. Bass may be a little less nice, but should work.
#3
Are monitors absolutely necessary? Or would it be possible to go without them...
Gear:
Ibanez GRG170DX
Peavey 6505+ Combo (60w)
Roland Cube 20w
Ibanez TS-9
Boss Chorus Ensemble CE-5
#4
The 57 and 58 are the same mics, just one has a pop filter ball on it. Same capsule is in both mics so you could use either one.
If you want to also capture vocals, go with the 58 but if you only want to record the amp, I would say go with the 57.

But yea the mic and interface are all you really need. Just get a mic stand and XLR cable while you're at it. This package will do.

Shure SM57 Pack
Shure SM58 Pack

As for monitors, most people say they are a must to have and you should get high end ones, but if you're not mixing songs and such, you could get by with a set of good headphones IMO.
I like the Grado Labs SR80s but the Senn HD280 Pros are worth looking into as well.