Indeed, assuming the manor's defences have been overcome.

Lands can be raided without dealing with the manor.

You are indeed allowed to upgrade manors and walls after the game begins.

I hadn't thought of a minimum, but I suppose there'd need to be at least a small minimum. Wouldn't make much sense for five guys with sticks to go terrorizing the countryside, and come back with the loot of everyone in the land with no resistance. I'll need to mull over a good minimum.

And I shall be excited to roll for them. <3