I have two full teams at 80 now so I already have everything except for an engineer... i've never tried engineering.
for my 5x pally team I'm working JC on all of them, got 3x of them doing the daily already and I haven't decided on any side stuff for them other than skinning.

you are going to need mining on at least one of your characters to support all of those engineers. I suggest a druid for this because of the instant flight you can mine a lot in a short period of time, the druid can do your herbs too.
skinning should probably take out just out of principle... you kill a lot of stuff you can skin in the game and make some money off of it.

if you have any mail wearers maybe a leatherworker.
if you have any plate wearers maybe a blacksmith.
with a tailor/enchanter you can make bags and enchant you stuff.