Tank for gear/augs. Everyone else for as many as as you can before silver, and a second I'd go zerker again for the augs/best weapon/heroics.
As said, get the rkii spells from marketplace for bard especially. Once you have the AAs, casters and healers are just fine in f2p gear. One month gold gets you 500dbc, I forget price of rkii but I believe a second month will cover that too, but you could stagger that out and get the rkii later on. A third gold would be bard for same reason as zerker but to a lesser degree(less impact on DPS via melee and heroics) All depend on if you have ToL or CoV or not as well, the best gear and aas on f2p are at 115(gear) and aas of course at 120.
If you have to stagger different months, go war, shm for aas to keep yer ass alive, then zerk to kill faster and thus live better, and bard for aas. The really expensive aas on bard are best impact I'm, bit bard can be quite helpful with just adps songs til you get him aas. Ideally you'll get shm maxed aas quickly then leave him silver and the rest gold as long as you can.
Gear/augs(for defense on war and heroics on melees)/weapons dependencies would be how I'd prioritize who is gold for extended periods of time as there's very little difference for castingtypes once you have the AAs, from top f2p gear per level to Max gear possible