Main thing is to make sure the cooling system, engine and gearbox are healthy. Get them checked properly including leakdown and compression. Otherwise when you blow an engine in your 2nd or 3rd event, it will quickly put you off racing! Then yes, if you plan on being competitive, don't cheap out on things like sumps or maintenance. Racing is expensive and S*** breaks quickly if you are pushing.
Talk to Sam though, he has managed to keep his car running over quite a few events, I suspect he has some mechanical sympathy though. And road tyres probably helps too. But doesn't stop him being quick.