Buy what you want and take it one day at a time. Learn as you go, trial and error. Plus we won't mind selling you parts in the future.
For real man, no answer will be the right answer! Especially buying a used quad, no telling what you'll get bro. So buy what you want and go from there. You can pretty much assume that a perfectly tuned banshee that has been mildly built will be reliable............maybe!?