Better to start off smaller and go up. So much to learn before stepping up to a big bike. It will make you a better rider in the long run.
250 vs. 500 is a good argument. Just get what you feel right on and dont sweat the rest. I have seen where people on 250s can run the piss out of them just because the lack of power. they are easier to toss around.
If you are making what you consider a big investment in this bike and can afford the Insurance. then go for it. Peace of mind is a good thing