I'm trying to gather intel before I buy a car, what should I know about motors and whats the difference between different motors?

 

how to do a compression test to check the overall health of the motor is #1

you can rent them for free at autozone, advance, etc.

 

The block stamp will tell you what block you have(B18C1/B18A1/B18C5 ect) there will be a number on the head like P72/PR3-4/PR3-1 ect. that will tell you what head you have. Wikipeda has all the engines listed:http://en.wikipedia.org/wiki/Honda_B_engine

There's VTEC heads and non-Vtec heads you can tell from the valve cover.