500 cc. is more realistic to learn on and even one of those with today's science can get out from under you so fast you will not know it until waking up in the hospital. I personally knew one fellow killed on a Suzuki GS550, he did not respect the bike, was a learner, and lost it in a single person accident.
A 750 is really too big for a learner. Problem is, the best size bikes for learners have pretty much vanished, the market is now driven solely by the long term expert rider.
Expect needing to clean the carbs to be the tip of the iceberg, people claim that when they can not figure the problems out and VERY common to be way more wrong with the bikes than just the carbs at those lower prices. Carbs are the first part removed when a person has no diagnostic skills, it's a male testosterone thing, we just can't NOT do it.
Not saying you can't do it but it will likely be a morass if you try. Like just the carb thing by itself, or why so many now say the carbs need cleaning. Today's fuel commonly has ethanol in it and it wrecks utter havoc on carb parts, commonly when you see that the 'carbs need to be cleaned' they are telling you if you read between the lines (you better if you hope to have any success!) that many of the carb parts may now be destroyed by the ethanol, which it commonly does when you let the bike sit with fuel in it. You will be doing more than just cleaning them and it's been that way since ethanol reared its' ugly head. It and vehicles that sit long periods are a bad combination.
Certainly not trying to scare you off but a healthy dose of reality is needed there. Having been 16 once myself I know that giving it some thought then making a plan can still work there, and likely better. Unless you already ride you just really have no idea of how fast a modern 750 can kill you. The 500s will too if you do not give them the respect they deserve, once you get some skills under your belt then it opens up quite a bit and you can then go bigger bike. We're talking life and death skills here, make no bones about it. I read once VERY long ago (late '70s?) that the rate that someone pulled in front of you while you were on a bike and YOU had to perform evasive action to avoid an accident when the driver didn't was something like once in every 160 miles and I had no issue at all with the number, now with all the morons on cellphones I wouldn't even want to think about it. I Just drove 12 miles to son's house this weekend and 3 times on the way had to do something when some loon (a different person every time!) drifted into me while on a phone and I was in a car. There are lots of idiots out there now. Bike? They will never see you, they can't even see a car. You MUST develop what I call 'jet fighter pilot' skills to see them and pre-guess what the driver will do and that includes more looking behind you than you ever thought possible. You will learn to instant scan driver faces to scrutinize their thinking much more than you do now. Or note how the car is floating (driver body language translates into car body language as driver lightly moves the wheel without even realizing it) around like he wants to change into your lane, you will get WAY better than a 50% guess rate on that or you will be in trouble.
I learned riding at 12 for what it's worth and on the 500s by 16, but we had learner bikes of under 200 cc. to get good on, nowadays you don't have that very much needed bumper. You can throw down on 100 cc. bikes all day long and only pavement rash and laughing over it, but a 750 laid down can kill you if it hits you right or you get tangled up in it going down. A 500+ lb. bike bouncing on you is much worse than a 180 lb. one, and the speeds are much higher too.
Look up the stuntgirl that just died making the second Deadpool movie, a perfect example. She roadraced but I hear on smaller bikes and had skills in that as well as movie stunt work. She did the stunt on a much bigger pocket rocket though and I'd bet a million that she just bobbled a bit while doing the stunt but doing that on a hi-perf big bike is death, if you grab the throttle as a reaction to losing grip for a second you just unleashed another 50+ hp on top of what you already had and instant loss of control doing it and what it appears happened. Those bigger bikes double the power almost instantly and nobody needs to be learning on them.
The 750s we ride here being older are nowhere near that in power level but the increased weights and speeds are still not to be taken lightly AT ALL.
Having said all that I wish you luck with your intentions. We welcome you but cannot tell you enough how careful to be. At least by your post you are clearheaded and think well, that will go far in getting it done.
If you continue down the same line there are people here who will go more than overboard to help you out..............