Given that .01/.02 on PStars is a $5 buyin, I'd say a safe bankroll for it is $100. $50 on it isn't the worst thing in the world, but I would certainly grind that up to at least $150 before moving up to .05/.10. Notice I said "at least".

If you're just starting out, I'd also suggest sticking to one type of game 'til you get solid at it. Meaning, if you decide to go forward with the ring game, don't do SnGs for a while - they're conflicting play styles and will likely mess you up. That said, the $1/2/3+0 MTTs on Stars are fun, and can be quite profitable if you happen to get real deep in 'em...just don't expect to get anything.