Not sure if you're planning to stick with playing on 888Poker but it's probably a great place to start playing micro cash. Know you can count on a winrate much higher on that site in micros than you'll see on say a site like Pokerstars
(or anyother site I've ever been on).
In all honestly a far more realistic goal would be to just try to continue to work at becoming a better player all the time. Then once you've played for awhile you will have the answer to your own question here.
(Can you eat on $500/mth.? my pets cost me almost that much).
Doing the simple math based on winrate, limit & amount of time you're planning on putting in, it works out to ~$154/mth.
888Poker had put a on a limit for maximum amount of tables to be played last I played on there which was 8tables.
I played there quite awhile ago, ran up a small bankroll from a freeroll cash up to just over $300, 14-tabling 2nl, just over 20k hands.(played for ~2hrs. each night, 3-4 nights/wk. for ~1mth. In other words, a ridiculous winrate which I believe is due to there being a huge number of completely new players, and am guessing many of them are sitting there with their 'Free$8'.. which for all I know they've grabbed for the umpteenth time, thinking they'll actually be able to withdrawl one day... til' they get caught. Pretty sure my guesstimates aren't far off). By comparison, when I played 2nl on Stars I think I had a winrate of ~10bb/100. BIG Difference! On 888Poker 2nl, it wasn't unusual to win 5 buyins on a table in 10mins. some nights. Just my experience but have also heard similiar from others.