what are the best styles to start in poker tournaments or cash
You can play pretty straight-forwardly in tournaments, most people play tight, so wait for good starting hands and play them aggressively (but be careful if met with resistance!)
I never really got into cash games but for beginners the cheapest way to learn is to short-stack cash games (treating them very much the same as tournaments). Playing short-stacked cash games will also prepare you for short stacked situations in tournaments.
Yes, you could jump right in and play 100+ BB games but the learning curve is steep and it could get pretty expensive! (Too much for my taste!)
150 buy-ins is normal bankroll poker professional.
Typically the PRO player not so many sources of income besides the game itself, so this
bankroll is a must, even in case of serious fluctuations to remain
stable psychological state and not to ruin his career.