I wouldn't worry about getting a 750cc or so. I'm 5'8" 175 and picked up a Suzuki M50 (800cc) for my first bike, the weight and size is not an issue for me.
Go to the dealers, sit on them get a feel for the weight/ size and I think you'll see the that it's not a big deal. I was looking at the Rebel (250) online until I went and sat on it and realized how small it is. Not that it's a bad bike, I enjoyed riding it in class but felt I would grow out of it too quick. I will have the wife on the back so I had some concerns about it handling our combined 275 lbs.