I personally wouldn't recommend selling your account.

Besides the fact that its against the EULA and Terms of Service, even if you were to start brand new accounts and not use the existing account any more, it can be very useful for you.
If you were to Recruit a Friend, say 2-4 accounts, you could use the existing account to boost your toons to 60 very rapidly.

15-20 Deadmines, 20-28 Stockades, 28-42 Scarlet Monastery, 42-50 Zul'Farrak, 50-55 Sunken Temple/BRD, 55+ Strat/Scholo.
Or pick another progression of your choice.

I don't have a very well geared AoE tank for boosting, but running a half decently geared dps toon..
I have Warlock (T5/T6), E.Shaman (T5) and BM Hunter (T4/T5), the Hunter is actually the easiest to boost with because of the strength of the pet.
Its pretty easy to get a bunch of levels.. 4x druids did 18th to 47th this weekend, and I only played Friday and Sunday... granted too many hours on both days.

Boosting rocks.




Multiboxing is a lot of fun.

Finding synergy between classes is good.
Half of the fun is setting up your macro's so they work the way you want them to.

There are different considerations, depending on if you'd like your team to be PvE or PvP or both.
A lot of people seem to like a PvE team for instances and a PvP team for BG's or Arena.

I'm messing around with a lot of combinations, just having fun with it.

Shaman's x5 (probably go Arena x4 with a friend or all 5 for BG's) and possibly put my Pally in with this group for instances.
Druids x4 (open spot for a tank for instances, thinking DeathKnight).
Disc Priests x4 (fun class, really hard to kill a disc priest in pvp, so trying to box 4 of them).
Hunters x5 (Farming/Daily machines..)
Mixed x5 (Prot Pally, Dream Druid, Demo Warlock, Fire/Arcane Mage and Shadow Priest for instances).
Mixed x3 (Plus 2 eventually... Death Knight, Resto Shaman, Rogue).

Tempted to try warlocks x4 if I can get them to 60 before my RAF expires in 3 weeks.
Hmm.. Hunters are 53.. Druids are 47.. Priests are 16.. might have time, not sure.