Are all bottom brackets the same size (universal/interchangeable)? So if I were to take a bottom bracket out of any (scrapped) bike, would it fit this frame? If no, then how would I measure the size of the frame's bottom bracket?
Also, If you could advise me to any super cheap but good cranksets (<$50), that'd be great.

This is a list of what I've compiled this far. This should be it, right?

Frame ($25): http://3.ly/MkkR
Fixed wheelset ($130): http://www.amazon.com/Track-wheelset.../dp/B003XF071G
Chain (~$10)
Crankset (~$40)
Bottom Brack (I don't know how much or which model/make. ~$20 new?)
Pedals (~$10)
Bar tape (~$15)
Saddle (~$15)
Seatpost (~$8)
Spray paint (primer, multiple colors, gloss) (~$20)