yes, good idea
I now already gonna say, that the last 3 weeks of June (Juni) I'm away with the scouts (And I will miss LoD verrymuch! :'( )
so, maybe there best is a third helper for if I'm away, ...
Well back to the topic:
A castle is a good idea,
I would give an attack bonus if you can destroy a castle
and defence bonusses, if you sent troops to the castle (if you're not the leader or owner of that castle)
What do you mean with taxes?