Here's what I do for buffing with my paladins:

Seals: On pretty much all my teams, I have a button for a 30 minute weapon enchant like seals or shaman buffs (and then another button for self-shields like inner fire, warlock armor, etc). I mapped Alt+1 to just send Alt+1 to all, so I can pretty much just put whatever 30-minute self buff I want them to cast there.

Blessings: On each of my paladins I pick one specific action bar slot to hold the blessing that I want them to cast on *everyone*. Blessings I use change depending on group composition (e.g. when I drop my 3 ret paladins for other players, it's usually sanctuary and kings) so I'd just move the right blessing into the spot on each guy if needed. I use the 10 minute versions even at level 80. Then what I do is enable Repeater, hit F1, click, F2, click, F3, click, F4, click, F5 click, disable Repeater again, and everyone is buffed.