Here is what i tell you.
I am going to suggest you to decrease BOTH the amount of CP and the cost of units. Why is that? Because right now the CP cost system looks ridiculous. Why would i need those huge 1500CP, 1800CP, 2000CP, if NONE of the units cost 1 CP/single fighter? Seriously, can anyone tell my what is the real difference between having 100 CP limit with each unit costs 1 CP/fighter and having 600 CP and all units 6 CP/fighter? Just so you can have nice big numbers in left bottom of the screen? That is pointless. BfME had reasonable unit counting, with cheapest militia units starting at 1 CP/fighter. BfME raised CP limit to 1000, yet even the cheapest units starts at aroun 3-4 CP/fighter. That is not an increase, it is simply an inflation. We don't need this.
What i suggest is to develop a consistent system with unit ranks where units of the same rank being roughly similar in performance and CP cost, with slight deviations, and each following rank being 25 (or 33 or 50, dont know for sure) persent stronger than previous.
The foolowing ranks are:
Militia-grade units - cheapes and weakest.
Militia-grade units come at 1CP/fighter for melee infantry, 2CP for ranged infantry, 3CP for melee cavalry, 4CP for ranged cavalry.
Regular grade units - regular army is not super powerful, but it is trained and disciplined.
Regular-grade units come at 1CP/fighter more than militia ones, so 2CP for melee infantry, 3 CP for ranged infantry, and so on.
Veteran grade units - contains of skillful die-hards who can certainly kick some big ass.
Same here - 3CP/fighter for melee infantry, 4CP for ranged infantry, so on.
Elite units - best of the best. Literally One Man Army units.
Elite units come at variable CP per fighter, but something comparable with heroes.
Heroes comes for 5 to 20 CP
Siege machines cost from 5 to 20 CP.
Brief check-list:
Militia-grade infantry
- Rohan militia
- Easterlings militia (balcloth maybe?)
- Orcs
- Goblins (yes, i know they are still just orcs, but this is for the record)
- Dunlendings
- Corsairs
Regular-grade infantry
- Gondor/Arnor infantry
- Harad army
- Isengard scouts
- Elite orcs (like Gundabad orcs)
- Men of Dale infantry
- Elven militia (maybe? Not sure elves would use militia at all, except in extreme need)
Veteran-grade infantry
- Isengard infantry
- Easterlings infantry
- Variag infantry
- Dwarven infantry
- Lorien/Mirkwood infantry
- Dunedain infantry
- Dol Amroth infantry/Fountain Guards
- Half-trolls (if there will be)
Elite infantry
- All Hero infantry
- All Imladris/Lindon infantry
Militia-grade cavalry
- Spiders
- Wargs
Regular-grade cavalry
- Spider riders
- Warg riders
- Harad cavalry
- Mountain trolls
Veterean-grade cavalry
- Rohirrim
- Gondor Knights
- Dwarven Battlewagons
- Lorien/Mirkwood cavalry
- Easterlings cavalry (if there will be)
- War trolls
Elite cavalry
- All Hero cavalry
- Imladris cavalry
As for the CP limit i think you should get back to 1000CP, or even to 500-600CP for normal mode. For epic battle 4000-5000CP sounds about right.
Concerning the unit size - i think the best balance was the Isengard in BfME, with their infantry units are of 10 fighters and cavalry units are of 5 riders. I still believe that size of units to be the most appropriate. For those who want larger units, you can add a compromise solution - add the ability to merge few units of the same type in one larger unit. Say, good factions can merge two units into bigger one, and evil factions can merge up to four units. This would be also an homage to the larger evil hordes of original BfME.