I use a Mamba Max and Feigao 9XL with 4S lipo. There are several options the one I use is one of the more budget conscious options. Check the 1/8 scale conversion thread here (2nd or 3rd page lays out some different options) or check www.rc-monster.com
. They kinda specialize in gas to electric conversions using high voltage batteries.
Your questions are valid but a little to broad. Start with some questions to yourself...like:
Racing, Bashing, or a little of both?
How fast do you want it to be?
Batteries .... lipo or Nimh. Strongly consider 14.8V or higher.
How much are you willing to spend?
Answers to these and other questions will get you to what you want. Heat can be a real problem with these setups if you get things that don't work well together. Take your time and ask lots of questions. I knew very little when I started my conversion but after working through it I am very happy with the results. There really are quite a lot of options so start with what you want it to do and guys will get you there! Enjoy!