personally I always want a bankroll of about 75-100, i've never run out of money on pp so far.

As for losing on online poker, I played with play chips for a loooooong time before going to real money. Its hard but sometimes you can find a table with players that play seriously (or actually know how to play). I honed my strategy there, deciding which starting hands I like and what not. After being frustrated by getting called by the worst hands and losing I went to real money tables. Also before "sitting" at a real money table, I scout the table for several hands, checking whos tight, loose, maniac. I don't want everyone at the table to be good, why make it harder to make money? Unless youre looking for a serious challenge. Also I always like to see a loose/maniac player with a big stack at the table to set my targets to.