I play with 10 cavalry heroes + 90 lancers + 100 xbowmen or simply 200 slave crushers.
Foot army is for sieges mainly: by the time archers have unloaded all their arrows on the enemy, infantry can take over easily.
Cavalry army is for money making or sitting into garrisons to scare enemies.
Usually fill my lords' armies with rescued prisoners, mainly mercs, and cannon fodders.
In my games for some reasons Swadia is always succumbing to Rhodocks, Vaegir getting steamrolled by nords and Kherghit / Sarranids just doing minor stuff and getting trades up.
Never get much casualties, if any I replace them with garrisoned units.
Then again I usually run around with 220 men, 20 being replacements so I never run out of soldiers