Common advice is to have at least a bankroll of 300 big bets, so for $.50/$1, you would want to have at least $300. As for moving up, you want to make sure you have the min bankroll for the new level using the 300 BB rule. Also, you want to make sure you are winning consistently over a large sample of hands. What a "large sample" consists of could be debated. I would say a min of 15,000 hands and I really think this could be argued to be on the low side. However, you can always take a shot at the higher level and move back down if need be.
Not sure what you're talking about 30+.