am sorry the reply took so long.
it depends on your control and temperament. i started with 30k. now i keep roughly 50k in the account. i noticed ( this is my case , it may be different for others) that if i have more money i get an urge to overtrade and this could at times prove dangerous, so i usually take a payout once in 10-15 days. which is refreshing because for a long time it had only been pay-ins with very rare payouts.