I do know as babies they are hissy and they have a temper
Bulls like to bluff and therefore like to hiss and even rattle their tails, in most cases it is bluff but they continue to do it as adults as well, also every snake is different.

The place I planned on purchasing from have CB 09 Yearlings.Can someone explain this too me please.
Obviously an adult that should have some good size, I would recommend asking questions on temperament.

From the caresheets I have read I don't really see a real humidity answer.I've seen from 30-40% to 50-60%. Rough Idea anyone?
Ambient humidity is all you need.

I know eventually I will have to place a bull in a bigger tank,but how long should would one grow out of a 30x12.5x12.5 tank?
Well since you are getting an 09 which is an adult you will need something large enough to house an adult. I keep mine in a rack with tubs that are 34 7/8" L x 16 5/8" W x 6 1/8" H