I would have to say I would go with a 650 on the carb. Make sure it is a blower carb or if not make sure it is boost referenced. You do not want to run into detonation with those coated pistons.
As for a cam make sure the lobe seperation is around 112. Call the cam company and tell them the rest of your engine set up and they'll get you one that will work well with them heads and still get you out of the hole.
As for right now stick with the 6 psi. as the stock pulley on mine made 6 also.
You can always move up later. Another thing with these smaller units they are turning fast and make lots of heat. So upping the boost may create other problems.
These units are great in my opinion. I have had no problems so far and I also have coated pistons with a little higher compression.
Be careful have fun.