I'm unsure about permanent stone forts, mainly because I don't know where to put them. Though I'll definately add Boiling oil.

Currently I don't have any room to add more faction symbols/units, so I can't add Wales (I thought the Welsh were under English rule very early on but according to Wikipedia they were independent until 1282).

I agree with you about the ballista. Also ballistas were very uncommon because the knowledge of how to make them was lost when the Western Roman Empire fell. Mangonnels were more common.

Since I didn't make the general/captain textures I can't change how they look without another texture mod.

You'd still need to transfer files because the changes in txt files has a large effect on how the mod works but it's only a very small part of the mod's size.