Ludi your castle is awesome, it reminds me of the Italian Presepe. Good to have someone who knows what they're doing to help with the lights! I started to play around with LED lights from the dollar store, they have clip on book lights which are fairly easy to take apart and splice the wire as needed, although it sounds like whatever you end up with will be more refined.
I've been slowly working through trial and error, a lot of errors and starting over (especially with the stairs!) I finally got the tree done, outside portion, a branch is going to be growing in through a window upstairs which needs to be finished.