Ok cool. One thing you could do is have a card for each unit type with stats, insignia, colours etc. Things to point it out on the map. Have a ton of chits/tokens for each type of unit and when they are on the map there easily distinguishable for other units. If you have 10 cavalry on one space, make cavalry tokens with a 10 on it so players know how many of that unit are there.
A simple combat mechanism that is in a fair few war games or normal board games is this. Instead of rolling dice, the number of units equals damage to the opposing faction. Eg you have 6 cavalry moving into a space with 4 cavalry from the enemy, your 6 beats their 4. You do 6 damage to their 4 damage you have 2 cavalry remaining on the space where the battle took place. So discard the number of units killed. Its and auto combat mechanism and a few games have this info hidden apart from what type of unit it is. You tokens could be double sided, one side with type of unit and the other side the number of that unit.
If players take it in turns to attack then this will give agency to all players.
I think this auto combat mechanism is great personally. Each unit type has a initiative value. Ranged units will always attack first, horse units second then melee units. Each unit will have a different modifier on what it attacks of course but that is easy to do.
I have a great interest in this post by you as I design board games. Nothing published yet, but I know a few things on how to design a board game. I will point you in this direction tough
https://www.facebook.com/groups/BGDLCommunity
if you use Facebook, this group is probably the best resource for all your design needs. I use it every day near enough. Join it, make a post introducing yourself and post your idea and ask a question or two.