starter bike???
Are you ready to go down on the street? It's not a matter of "if", but of "when". And it probably won't even be your fault.
I've been riding for 30+ years and originally had the "won't happen to me" philosophy. It did, and it has 3 times and only 1 was my fault due to stupidity. The other 2 times were due to other drivers.
Luckily I've never been hurt.
But to answer your question, I suggest you take the rider safety course FIRST so you'll have the basics and know the feel of a clutch before you get on a bike and ride off into traffic.
I also suggest you borrow a friends street-legal small-displacement dirt bike if you can and get a few hours of experience around the neighborhood before you jump on a bigger street bike.
As far as size, I started on a 500 and graduated to a 1000 about a year later. You want something with enough power to get you out of trouble, but it will also have enough to get a new rider into trouble.
Just remember one thing: the clutch is your "eraser". Grab it whenever you feel you're in trouble. It cuts the power to the street and lets you get back in control of whatever situation you may find yourself in.
Also, don't scrimp on a helmet, jacket, and gloves. Wear a $10 helmet if you believe your brain is only worth $10.