When I started 10-boxing I used a DK tank and paladin tank. I discarded the DK tank and have never regretted it - the tanking style is just too proactive and not very macro friendly. Plus you won't need two tanks for every situation, DK's only offer a melee off-spec, and that may be an added liability. I have no experience with druid tanks, but on the surface they seem viable depending on how well rage works with a macro, not to mention they can be used for either healing or ranged DPS when not tanking. As I have no experience with them as tanks, I can't make any statement on whether or not their threat cycle is macroable.

For healing, you'll want two main healers and an optional third healer. I find it best if the third healer can work off of a macro that you can forget about, something that focuses on the main tank, but that's just my preferred style. I like the idea of matched healers for the two main healers - for example a pair of priests for their excellent AoE healing capabilities. I see no immediate problem with shamans and paladins as multibox raid healers, but I don't have experience with them in that capacity. Druids would be my last choice for healers. Much like DKs for tanking, druid healing seems more proactive in nature and that additional level of management is something to avoid.

Finally, for DPS, I'd try to cover all major buffs. Stick entirely to ranged else you'll be dealing with added mechanics in many fights and that will be ...annoying. All classes are viable to some degree, but my opinion is that hunters and shadow priests come with the most severe limitations. Shadow priests are disadvantageous because their DPS cycle has an overly lengthy ramp up time and one of their core abilities ( mind flay ) will consistently break auto-follow and change your character's orientation. Hunters are a bit worse - in addition to a pet, which will potentially soak up healing and die alot, hunters also consistently break auto-follow and change character orientation. They have proactive threat management, and a limitation on the range of their attack. They also don't have a very synergetic relationship with other ranged DPS given their damage is physical.

All of the DPS classes also come with limitations, but with the experience I've had, the two classes above are the only two that make me want to avoid them at all costs. As an added caveat, I can only relate what I've actually tried, experiences may vary. What works for me may not work well for other people, I'm far from an expert on multibox group composition. I wouldn't have thought a melee group was viable for 5-boxing, but people have proven me wrong many times over.

With the group you've planned out, I might suggest dropping a druid, taking one of your DPS priests and converting it to healing. Drop the hunter and replace it with either another warlock, moonkin or shaman. If you don't mind leveling another character, I'd replace the druid tank with another paladin for the additional blessing and aura offered.