Depends on your confidence in your own game, and your experience of 'swings' in your previous bankroll. (obv. they should be less severe now you've got a better grasp of BRM and have invested in Harrington etc) but for SnG's, an aggressive stance is 25/30 buy in's ($50+ would be ok for that) and a very conservative aim is 100 buy in's (so $225).
After reading your previous posts and seeing your serious about sticking to your limits, I'm pretty sure your ok with $150. Thats just over 65 buy in's for where your at. You could even chance odd $3 games (I think Tilt only run the KO game at that level though).
As was mentioned above, i'd drop it slightly for MTT's, there is far more variance playing those, larger field means plenty less cashes there than in sit n go's.
I'm not trying to tempt you out of your current level, but its healthy to take the OCCASSIONAL step up. What I mean is, dont burn out just playing the $2 games, have a pop at the $5 once in a while. Just one game to break it up. It also prepares you for the standard of play at the next level.
Tilt run the 'Token' games, and i'm fairly sure there is one at the $4 point. 9 seats, winner gets a $26 token and 2nd gets a tenner. Worth a look, as these are the only chance you'll get in the near future to play either the $26 SnG's, or the juicy MTT guarantees (about half of them are a $26 buy in).
Also, while I remember, there was a similar thread to this a while ago where it was mentioned that a 'brm' is only really implimented once you've reached a level you would be unable to re-deposit at.
i.e. if you are able to put $50 in again after you've gone broke, without really missing it, then by all means take risks by playing higher stakes to build your roll first. Some people will regard $50 as a bankroll, others consider it just a bit of playing money and will only impliment strict rules as far as buy-in's once they hit a few hundred.
Hope this makes sense, and helps. Congrats on last nights win's by the way! GL