Good on ya for learning a bit before taking the plunge. Twist of the Wrist is good, but Code's writing style isn't the greatest, in my opinion. THE absolute BEST book for riders of all skill levels is the one by Nick Ienatsch.
Inkaddict is right. You will never, ever, ever get the full performance out of a 600 on the street. It's just not going to happen. Most people can't even fully utilize it on the track, FWIW.
Trackdays are some of the best money you can spend. You've got some decent tracks within a reasonable driving distance. Nelson Ledges, beaverrun, Mid-Ohio... maybe a few others depending on where in PA you are. You will learn more doing a single trackday than you will in an entire season of streetriding. sportbiketracktime.com has an amazing beginner program with a lot of very fast, very competent instructors who will take the time to show you the ropes. And it's included for free with the trackday.
A 250 will be just fine, and there are even a few race classes with WERA specifically for it when you start to thinking you're getting good.
a 250 will also be cheaper to buy, WAY cheaper to insure, and you'll probably be able to sell it for darn near what you bought it for when/if you decide to move on to something else.