My first team used the super easy, but not as flexible as I'd like...
Everyone /focus Active Toon
Everyone /assist Focus .... /cast Spell.
That was relatively fast to set up, but still took some time.
I could set up a new team like that, extremely quickly these days.

Moving to a party based system took a while to figure out.
In particular getting follow to work, took a bit of time.

During RAF, in addition to my initial team, I did:
4x Elem Shaman, boosted by a 70 Shaman.
4x BM Hunters, boosted by a 70 Hunter.
4x Disc Priest, boosted by a 70 Priest.
4x Balance Druids, boosted by a 70 Shaman.

It took about an hour to set up each of these teams.
I've used the same basic toon switch macro's, which now is copy/paste, and insert the new toon's name in the macro.
Jamba covers follow for me, but it takes a moment to add each toon to a team, and set up configuration of the addon.
The macro's are pretty easy to set up, with two basic varieties now.
A) /assist [target=party1]; /cast PewPew
B) /assist [target=party1]; /cast [help] Heal Spell; [help, target=targettarget] Heal Spell; [target=player] Heal Spell.
With the party system, every toon needs an assist version of each macro and each needs a non-assist for when they're the leader.

Half the time, is moving things on the UI, which would be the same timeframe for a new single toon.
I have a window for spam that I occasionally view. Another for guild. Another for party. Another for whispers.
I like my damage meter in a place, Jamba window in another. Configuring Dot Timer takes a while, but it is incredibly useful for boxing.

Moving from 5x Shaman's and 4x Druids towards...
4x Shaman's + 1x Paladin and 4x Druids + 1x DeathKnight will take a little bit of configuration.
Basically move the damage spells to some hotkey numbers
And clear up a few keybinds for tanking macro's which I'd want to click independent of the dps.
Overall, having built several teams now, it won't take overly long to do.