I want to add a dumb yet fun army idea for unit promotions I had while I read all the replies:
Promoting units to as many of one class as I possibly can. For example, I make Amelia, Gilliam, Frank, Forde, Kyle into 5 Great Knights. The addition of Duessel will make 6.
And then I make Lute, Artur, Moulder, Ewan into Sages. Saleh joining in would make 5 sages. Etc etc.
Sure it'd lack unit diversity, but a raging stampede of 6 Great Knights sounds awesome and hilarious.