whats a sustainable winrate for a good player at 2nl, 5nl, 10nl...

im trying to calculate how long it is going to take me to work up to 25nl (20 buy in rule), where i'll start using the 20k hand rule

20k hand rule ? Are you going to start with 60$ (=20*Typical min. Buyim NL2) ?

Depends how good you are. I often see 7ptBB/100 as a good rate at low limits, but this mught be for 100NL and such. I am at about 6BB/100 at 25nl over my first 10,000 hands. I'd played limit for a couple of years but just started NL, and seem to do okay just playing ABC poker. I imagine if you are just starting but have some idea what you're doing, and don't spew off lots on bluffs and tilt, 5bb/100 should be pretty doable at 10NL and under just playing solid straighforward poker.

Also, look into bonuses that you can clear at those limits, as they can add a lot when starting a bankroll, and try freerolls etc. Don't know if you can clear any bonuses that low, but at least at UB you get a little something playing real low. I just played an Empire bonuses that clearde at 10x any raked hand,so a $.05 rake at 10NL would count, and it would be easy to clear at any limit.