It also depends on what kind of racing. You can be a tard like me and be a tree racer (harescrambles). Depending on how big you are, you can get away with stock width on the track, no rules against how narrow you are only how wide. I run 22's on the rear so a built motor is a kinda nice if you want any form of hill climbing power. Skids are a must. Nothing ruins your day, pay check, race or attitude like a hole in the case/countershaft getting ripped out.
Usual rules for all forms of racing: Proper protective gear, tether switch
My set up is a 240 with a mid range power port job, 22 kenda bear claw rears, skids, pro armor tether. Stock width, but that is only because I run in the woods and being narrow is a major advantage at the rutted up XC properties