Going from a rental to a Leopard/Rotax is huge jump up.
It’s kind of like going from your normal riding lawnmower to attempting to mow your lawn with a Camaro.
At first, things will feel like they are happening waaaaay too fast and you’ll probably have a few offs or spins, as we all did, but you’ll eventually adapt.
Starting off in a single-speed kart will make your learning curve much easier and make you a better driver quicker. Learning to conserve momentum is a valuable skill that can get lost easily if a newbie jumps into a shifter immediately and has all the power in the world at his disposal. I’ve been to many-a-club race where my slightly above mediocre driving prowess and measley 20hp Komet has outgunned newbies with shifters and twice the horsepower. That isn’t a boast on my part (maybe a little), it’s mostly to say that you need to learn how to apply the power properly before you jump into the deep end, and the best way to do so is to learn on something slower that requires you to be buttery smooth in your driving. Not to say you couldn’t handle a shifter, I don’t know you or your skill level well enough to make that call, but in nearly every situation, I’m of the school of thought that newbs should start in the slowest class that will keep them entertained and work their way up.
And as stated, Rotax’s DD2 engine is the 2-speed Rotax. Kind of a cool concept that isn’t super popular. A bit of a niche thing. Stick to something you can race anywhere with decent competition and you’ll be much happier in the end.