Well when counting units you rather forget TW series because you are not able to have army made just from best units like in TW but just opposite, most are irregulars, some militias, even less sergeants and just few elites. Also you have 30 cards but ten of them are just reinforcements I guess, before the beginning of battle you can choose which 20 of them will be ready for battle so you can make a tactical decision of army composition when you see whom you are going to fight but not all 30 units are available from the beginning I think. I am not for 100 per cent sure because I played just few battles since I was able to have more than just 20 units because I am now waiting for new patch because I got too often ctd´s lately. Also you mounted version of foot unit has half size. So for example if your perhaps level 15 hero can have 10 irregular units (melee 250men at max, archers 130), 5 (dunno now if that number is precise) militias (200 melee at max, archers 90, cavalry half size), 3 sergeants units (100 I guess melee at max, no archers if cavalry half size of melee) and one unit of elites 80 at max if foot knights plus your general bodyguards 50 at max (hopefully correct dunno for certain) you cant count how much its would be then.
Hopefully some clue (not precise but hopefully not far from truth) for your answer.