[mivayan]

I think that for placement of a castle, you can ignore indie troops, chokepoints, neighouring enemies etc and just focus on maximizing resources for national troops. The other things are too hard to get right, but maximizing castle resources is easy.

for each province I own:
if I build a castle here, what will the combined resources in all castles be, assumin no provinces changes owner untill it is done.

Then pick the province with the highest result.