Multi-room in-ceiling positioning

Hello everyone,

hopefully I'll get a better luck in this section (in speakers I've got no anwers) even though this is not a home-theater design rather a multi-room system.

I'm planning a multi-room system for a new conto apartment (Euro size apartment), ceiling height is 9,2 ft. As you can see in the picture attached I have:
- n. 1 studio (130 sq. ft.)
- n. 2 bathrooms (75 to 80 sq. ft.)
- n. 2 bedrooms (135 to 160 sq. ft.)

Main listening will be background basically in every room, maybe with the exception of the studio, where a more "serious" listening would be nice to achieve (not mandatory though). Please note that I have a large living room where I have the best critical and serious listening experience with floor-stand speakers. I've planned to use a stereo speaker for each bathroom, while in the other rooms a couple of speakers. Sources will be mainly music streaming services (e.g. Spotify and radio).

Q1. Do you see any major issue to where I position those speakers? Basically I position them at the center of each room, with the goal to have the whole room covered.
I've read different in-ceiling speaker manuals (e.g. B&W, Russound, NuVo, Kef, etc) and they seems to have different point of views on where to put in-ceiling speakers, that's why I would like to have your opinion on this topic.

Q2. For the studio, do you think tilt-able/pivotable tweeter might help to achieve a more "serious" listening and enhance imaging and staging?

Q3. Do you think 6,5 inch speakers might be enough for a background volume level listening or I might have way better results with 8 inch speakers? Of course I will have more bass, but I would rather spend more on better 6,5 inch speakers that go down a little more.

Any help is very appreciated. Thank you so much.
Cheers.