Hi Martin,
1) Yes, I had an electrician bring power across in a trench. However I had it come up under the scope rather than in the bay. That was just because it was a bit hard to figure out exactly where to bring it up so that it would be right next to the bay wall. Also, if I later changed the bay location, it would be a problem re-locating the power. With the power in the centre, I can just run an extension across the floor to anywhere I like. Then I have some power boards stuck to the walls.
2) Yes, it's single layer so running cables can be messy. I'm sure it could be done neatly with a bit more effort using cable trays or conduit. But the single skin walls are good for temperature equalisation. It cools quickly one the sun goes down which is what you want.
3) As per (2), it cools quickly so it doesn't stay hot inside once it gets dark. I've got a floor fan in there to speed up the cooling but it's probably not necessary.
4) I think it would be ok, but it's hard to be sure. If you're on Facebook I would suggest joining the Nexdome User Group and ask the question there. I'm sure someone has tried a scope of similar size.
https://www.facebook.com/groups/477732789267400/
5) Yes, I bought it from Siderial Trading. No complaints.
Peter