In an another topic, for the knight, (in the next version) why not make it like in Stronghold 2, like the knights are on foot and on horse, then make the horse with more armour like the cloth for the knight's horse, then with the lance when mounted.
Then, for the crossbowmen, make it a little bit of a reloading speed, but have more damage, as in, their arrows can penetrate metal armour, and their armour is leather, then slower than archers.
Then, for siege engines, make rams, trebuchets, and if you make this one, a mantlet (has high armour and health, cannot attack but it can act as a big shield against enemy arrows and projectiles, also, make it vulnerable to melee attacks.)
But for the walls, they are unstable connections with other walls.
Thanks!