A guildie of mine who is just getting into boxiner again (only 2 boxed a bit before) used his 80 hunter, and boosted all the way, doing VC, then Stocks, then SM then ZF, then BRD, then Strath. I think he opted for more instances so he wouldn't have to deal with the huge aggro radius from bringing in the lowest lvl possible.

If your end goal is to 5 box, you could just level them together, learn the ins and outs as you go. But since the game only gets interesting at 60, I see no harm in boosting to 60 then playing as a 5 man team. Hell, boosting to 70 then running 5 to 80 would get you pretty far.

As for the boosting 4 toons at a time thing, ask yourself, what do you have more of, time and patience? or money? If it's time, just boost the shaman, then quest the paladin, with the shamans assisting in DPS out of party, and party up for instance quests.

If you have more money than time, you might consider ditching the 2 of the extra accounts, making 2 new RAF accounts, and either transferring the 35 shaman (not worth it IMO) or just boost from scratch 2 new shaman, and 2 other toons you'd like someday, and gift levels once you hit 60. You could also gift levels to a paladin and xfer him to the main account and just forget about the original. Once you start brainstorming, you can come up with a ton of different scenarios for utilizing RAF. Just make sure the hunter is on a separate account from the 4 accounts to be boosted.