I used to three box when i first started (three shaman) , its was good for lvling in the random instance ques because i could focus just on DPS'ing and nothing else. Since then ive only got one more account, so i have 4 shaman and now i can que one as heals + 3 dps for instances and a friend tanks . Id like a 5th account but im not sure if i want to lvl another toon yet.

4 Lava Bursts are better than 3 in pvp, 5 would be better, but just play with what you want. I know a few people that 3 box and they hold there own in a bg very well.

Have fun and good luck on your new team.