It’s generally advised not to start in shifters. They are quite a handful and it’s really easy to develop some bad driving habits if you start with all that power. Starting in a slower class will develop your driving and make the learning curve much easier.
A TaG kart (Leopard, Rotax, X30) is going to be around 30hp whereas a KT will be between 15-20 depending on exhaust and carb setup. On most tracks the TaG class is 2-5 seconds faster per lap.