Blues have posted, Beacon will likely only work with the fast/expensive Flash of Light heal, in Cataclysm. Two for One healing will be too strong with efficient heals.

I know you can macro Rejuvenation, to hit the entire party. I'd imagine it wouldn't be overly difficult to set up macros which HOT the entire raid. Not sure on the boxing side, but a lot of PvE one-box raids have so many healers on the tank and the rest on the raid. It might be an idea to go with one raid healer and one tank healer, and perhaps a third healer option for when a second tank is required. This is of course speculation, as I don't 10-box.

Two Paladins will have sufficient buffs to hit everyone with blessings. But I don't think only two pallies could cover all of the auras, although two should be plenty for most encounters. Healing options are: Druid, Paladin, Priest and Shaman. All of these bring a decent DPS spec, although the Paladin has to be melee if they're not a healer. Having the option of dual-spec for some of your toons is a decent idea. Most of the time, you'll need two tanks, two healers and six DPS, but sometimes more healing or less tanking.

Overall, I would try to balance so you have all the raid type buffs between your toons. After that, ideally you would have an even number of toons using each type of drop.