I have 6, and have them laid out in this fashion:
Healer Acct
DPS Acct
DPS Acct
DPS Acct
DPS Acct
Tank Acct


This allows me to pvp effectively (healer+4 dps), instance effectively (healer + 3dps + tank), and do other strange things (4 dps + tank -- which is how I leveled)