You can have more if you up your settlements or ressources building, the maximum troop I had was around 20 000 CP by playing Mordor.
If my memory serve me right I had 18 000 Orcs (Normal, Minas Morgul, Cirith Ungol, Dol Guldur) 1 000 Troll with armor with Tambour, Grond, Heroes, my personal hero, and 500 catapults Siege Tower and ram.
let just say When I unleash all of them to show the Almighty Power of Sauron on my enemy my Computer crash with the message Out of Memory.....
Conclusion :
You can have a big army but never use all of them in the same time, the amount of data the computer need to manage is too much T_T.... 3h to play for nothing
Another skirmish I had 20 Mumakil, and 20 000 Haradrim and Easterling thanks to a special map. I fall in love to see my army
and victory at my hand