... I don't agree with starting on a 250-300. I find them underpowered. With that bike you also need to know how to open it up hard to get out of sticky situations. Unless you are just riding on 50 roads or around town. ...
You can find yourself in sticky situations on any size bike. Opening it up hard to get out of them just makes it worse if you don't already know what you are doing. I *very much* advocate starting small -- less than 30hp is best. You have to learn how to *avoid* sticky situations. You have to learn to look ahead, plan your moves and passes, be in the right gear and keep your engine at its peak, conserve momentum and keep your corner speeds up -- all the skills of a good rider. If all you want is to be able to ride well enough to get to the bike night at Starbucks, you can start on anything. If you want to be a skilled rider, start on a 250 and stay on it for at least a year; two is better.
... And it's not going to give you the power-handling experience you will need if you plan to just straight to a liter bike or even a 821 later ...
and of course the answer to that is to not go "just straight to a liter bike or even a 821 later"; your second bike should be something midsize, like a 500 or 650, smaller Monster, older 750, etc. Spend a year or two on that. THEN get a big bike if you feel you really want one. One thing the mid-size bike can teach you is that you don't "need" a big bike. With modern performance, *nobody* NEEDS a big bike on the street. You may *want* one, and that's fine (especially if you have taken the time to develop the skills). But 75hp is more than enough to handle anything the street has to offer. I've ridden quite a variety of more powerful bikes, up to 200hp, but my old M900 Monster, with its 75hp, has plenty for real life. There are times when more than that would be fun, but in the last 22 years of riding it, I have never actually needed more than it has to offer.
... I'd suggest Ninja 500, Suzuki 650, or ... I'd say your size and weight should play into your decision in the sense I wouldn't start out on a bike I can't pick up off the ground if I drop it somewhere remote.
Taking your size and weight into account is a good idea. Pretty much anyone can physically handle a 250, though. Starting on a Ninja 500 can make sense if you're a larger than average person; if you're 6'3" and 250lbs, yeah, go with the 500. I don't recommend the 650, or anything that powerful or greater, for *any* beginner.