I'm glad you're here "brain-storming" this project- the discussion is bound to help others doing similar projects.

I'll toss in another idea: When I think of the weight & hassle (to water-proof & keep in that way) of building with wood, I'm wondering what else might be used instead? Mind you, I'm not a builder, but I was wondering about the strength of those vinyl fence posts if used as a framework- they'd be easy enough to drill & attach things to. Just a thought...

https://www.lowes.com/pd/Freedom-Com...k-Post/4009495