simple rule: Don't withdraw single cent if you don't need it.
It doesn't matter if you have 1000 or 5000 BB bankroll. The more you have the better for you, so you don't need to move down during the huge downswing.. I use to keep only 300-500 BB in my poker client and the rest on bank account made specialy for poker related things (software, books etc.). Calm me distrustful, but I prefer to not get bankrupt if someone/something hack into my account 
If I need to money, I just make transfer from poker bank account to my personal one: it's instant because I have them in the same bank. Easy..
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Your second question is bit more complicated but I'll help myself by using BRM excel sheet made by one of the DC coaches. It's simple .xls file without any formatting, because I didn't have time to play with that. You can download it here.
Short introduction:
- put values in blue cells / white are calculated..
- number of hands: amount of played hands on certain level lifetime
- winrate in bb/100: lifetime again
- rakeback: your average rakeback in BB (27% on FT, 15 - 40 on Stars... - you have to count it on your own)
- SD in BB/100: standard deviation - it's still not implemented into PT3 (should be soon), but can be found in PT2.. no idea if it's in HEM or Elephant. If you don't know it, 17 is average for SH (i had 15 on 0.5/1 and 17 on 2/4) and 13 should be OK for FR
- uncertainty: what's the dispersion of your net winrate.. (or something like that
it's not important)
- Confidence: e.g. 95%: it says, that with probability of 95% is your real winrate higher then upper value (0.5 in file I sent you) and with probability of 5% is higher than lower value (2.5 here).. it depends mainly on amount of played hands + somehow on deviation
- big bet: BB in you game
- Risk of ruin: you can choose anything from 0.01% higher (0 is not possible of course)... it determines your required BR in next steps
- Recretional Bankroll: minimum bankroll you need if you're playing for fun (you don't need to withdraw anything)
- monthly nut: what are your monthly expenses
- hands per month: your average hands/month on this limit
- professional BR: it depends on same stats as recretional, but it now counts monthly nut + hands per month
- living reserve: min. 6x monthly nuts (it's up to you)
- starting pro bankroll: pro BR + living reserve of course 
hope it helps; if you have any question, feel free to ask