Read the article on why a 600cc is a bad idea, listen to the other experienced riders here, including many who currently own a supersport. Just avoid it for a first bike.
Instead get a nice used ninja 250r. pre-08 ninjas are usually less than $2000 and many are available. You can learn and thrash on that bike for a year or 2 and if you decide to upgrade you will lose little on the sale. The 250r has enough power to exceed any speed limit in the US and can out accelerate most sports cars from a stop.
Other good choices include the GS500F and ninja 500r. A little more expensive and not as common but you still can probably find some good used ones without a problem.
Don’t think you have to get “the bike” you will keep for your first bike. In fact that is probably a bad choice as you don’t yet know what you really want. It seems no matter what bike a person starts out with he ends up changing bikes 3 or more times in the first few years of riding. You might as well start out on a cheap bike that is easy to learn.