I think it's good to start on a 600 especially since you've ridden bikes before. My first street bike is my cbr 600 and as long as you choose not to drive it out of your limits than you'll be fine. One of my friends got a 250 ninja for his first bike and he sold it in a month he wants a 600 now.
Yeah, don't ride out of your limits. Any bike, or scooter, can kill you. As my dad put it, run your head into the wall at running speed (~4 mph) and tell him it doesn't hurt.
I would never tell anyone to start on a 600, However if they have riding experience whether it be dirt or street and know not to go beyond their limits at first then it's all good.
Just wear your gear, Ride smart & don't be a douche :mrgreen:
One of my friends that never lets ANYONE ride his bike has a cbr 600 and we were just sitting there hangin out and he told me to ride his bike (Whenever i've never ridden a street bike ever). I was like uhh forreal lol. He was just like yeah heres the key just wear my helmet. I was like ok. Just rode around and than I ended up getting one lol