If you are just starting to race get whatever suits your wallet. A super fast engine can be a liability until you learn to be fast. An OS TR (not sure if these are still available) is cheap, plenty fast enough, reliable, easy to tune for someone just getting into it. King of the carpark doesnt usually transfer to king of the track. Get something reliable & not too much grunt & you will have more fun. You will know you are ready for more power when you can lap consistently for a race without hitting anything. Then get a nice RB, Nova JP etc.
BTW good choice on the chassis, the 720 is a great car.