You may want to step back and think about what you really want to DO. If you only enjoy leveling then yeah leveling all those teams in various combos (tank, healer, DPS is basically the best) in quests & instances will be a blast. It'll take probably a year to get em all to 80, but things will be different enough.

End-game in WOTLK is very rich, there is a lot to do although most of it you can burn through in 4-8 weeks of daily play -- namely getting a few (5-8 new ones) factions to exalted for items/recipes, running all the heroics daily for badges/shards, buying badge gear (about 200 badges worth of good gear to buy atm, more in future patches), Wintergrasp PVP fun, dailies, profession dailies, leveling profs to 450, etc, etc. Its pretty extensive and I spend 2-3 hours a day on just a single team and cannot come close to getting everything I want done. Not sure how you could possibly do it with multiple teams.

Not to mention the raid zones in WOTLK are fairly easy and you can pug them all, unlike TBC. I haven't yet multiboxed all of them, but every single one of my characters has cleared every 10 and 25 man raid zone except Malygos. Its a lot of fun seeing all the raids, Naxx25 can run anywhere from 3-8 hours so its not super short - the other two raid zones are each 15 minutes or so however.

Point is you may want to seriously consider just picking one team, leveling them to 80, running heroics, getting reps up, doing raids, etc. That will consume virtually all your play time for at least 2 months. By then the next major content patch might be coming down the road, which will definitely have a new 10/25 man raid and may include new dailies, faction, 5 man, etc. I'd guess we'll see the next expansion in 12-16 months as well.

I leveled ~15 toons to 60 when RAF was active (one team per weekend basically) and virtually all of them have sat at 60 for the past 3 months Even now I doubt I'll ever touch any of them, I am leveling a single Deathknight to try out the new class, but theres always some heroic I want to run on my main team, and then Wintergrasp goes hot, and then...