I'm not gonna sugarcoat this. A YZF600 is too much bike for a beginner. Don't rush into trying to keep up with the experienced riders either. And don't rely on the bike to do that for you. An EX500 is a great beginner bike, but on twisty roads in the hands of an experienced rider it also can keep up with most bikes.
As for your size, I'm 6'4" and weigh 220 lbs, and I did quite well racing an EX500. It's a lot of fun ducking under four-cylinder bikes on the inside. Obviously, the top-of-the-line 600s are faster and handle better, but it comes down to skill.
Kudos on taking the MSF course. You've got a better start than a lot of people. Take it easy, and have fun.