Hi
Re the Empress range, it wasn’t designed to fit in with Warlord but it is, by chance, fairly close size wise (and can work with Assault Group to). There are, however, differences in sculpting style and (in particular compared with Warlord) casting quality 😉.
Looking at the actual packs within the range, nearly all the horses have pistol holders on both sides of the horse but you can get a pretty irregular look mixing helmets (the ones in burgonets might be particularly useful?) with soft hats etc. Also have a look at some of the dragoon figures (particularly the command packs). Be aware the “rank and file Dragoons’” are on nags (as they should be!) rather than full sized mounts (note, the dragoon officers are on normal sized horses!). There’s also a mounted command pack with a bearded officer in 3/4 armour but wearing a montero, I’m currently painting one up as a wizened Royalist Foot Brigade commander but he could happily fit in as the local squire leading his hastily raised troop into battle?
Have a look around and see if any of the range works with what you’re planning?
EDIT - just seen Paul’s comments re the dragoon nags that he put on whilst I was typing this reply. Yep, these might work for really poor quality mounts given what you’re planning?