System planning
Been researching. I would not recommend mixing type of speakers for the fronts. You may find that the on-walls are just not feasible. A center on stand on mantel is about 7” high. I think a 42” plasma w/o stand is about 26” high. If you decide on in-ceilings, make sure your architect/builder are aware for placement purposes.
Many manufacturers offer some aim-ability. Speakercraft offers the most flexibility with 17 degrees plus additional 30 degrees for tweeter. They are also a quality speaker. The AIM line configurations are the same (8” woof, 1” tweet), just the materials change as well as pricing. The AIM 1, 2 or 3 ($425, $625, $825/pr.) should work very nicely for you.
As far as receivers go, most mid-fi ($800+) 7.1 receivers offer 3 “Zone”/source capability. Since you are planning a 5.1 HT, you are able to use the extra 2 rear channels to power Zone 2. Zone 3 requires its own totally separate power amp. Some Yamahas have an additional Zone 1-B configuration option. What sort of configuration you set up really depends on how flexible and independent you want the system. Basically, you are planning 4 areas with 3 zones. Are you willing to combine 2 areas using 1 Zone/source? Ex. I have 3 areas (2 bedrooms, 1 outside) with volume controls on Zone 2.
Hope this sheds a little more light.