I have a suggestion or two...
1: Include all races, pinks, yellows, orcs, the whole bit.
2: Go with a lot of cheap slapdash vehicles, stuff that could be kit bashed from found parts in a few man/hours of Minifig work.
3: Do not give your troops uniform equipment, mix muskets in with rifles and wizard lightning staffs, keep the categories the same across the unit but otherwise mix it up as much as you can.
4: Go with a quality over quantity approach for troops, the militia in the stories are always outnumbered but win anyway.
Just my 2¢