Go in wall or in ceiling. If you look on Audiogon, eBay or even Amazon there are so many speaker bundles that they are fairly cheap. It just gives such a cleaner custom look. Be careful of surround speaker height. If in wall facing forward they need to be quite some distance behind you to be effective. You can mount them low in wall or ceiling bouncing off the rear wall. Look for ones with an amiable tweeter. Look around audio equipment is marked up so much you will be surprised what you find for 75% off retail that will work. In a second bedroom we did a set of Jamo from Amazon that were $125new and sold for approx$800 when current. They are decent and have a cool look being ball shaped. Point is look audio equipment dates quick and have steep discounts. Subwoofers are also a concern regarding placement as loading a corner can get boomy fast. I know audiophiles hate Bose but a marked down or almost new set up is one button use family friendly and in a large room they sound decent. Sometimes the family just wants to watch a movie not play with mismatched components.

If you have the space to spare, you could set up a different room as a media room and keep the big black box out of the main living room (you could instead use that space to read books/play games/converse with your family and friends). Or you could have one space with a TV and one with a projector for movie nights, so you don't have a screen taking up wall space all the time. Whatever you do, do it because it works for your own actual family, not what someone else has done in a different house.

Not much I'd do differently overall. But here are a few things; I would use rubber under the wall framing to isolate it from the concrete floor. I would try even harder to find someone to replace my wood support beam with steel. At least one long enough to remove the support column in the front of the theater, if not both. This would be more for aesthetics than performance. I did try over a dozen different contractors with no luck. They either did not have the time or they lacked the ability. Being able to decouple the ceiling would have been sweet but there were just too many things to work around and I would have lost at least a foot in ceiling height. But even decoupled bass is going to escape when playing at reference levels. Mids and highs are pretty well contained within the theater. I am running 2 Denon AVR's to get 9.x.6 layout. Still waiting for a reliable 9.1.6 processor. The 2 processor set-up is not perfect but it does come close enough to make the waiting bearable. I am running 3 18" subs up front and 4 15" subs in the rear. I have 6 12" subs under each seating platform (total of 12) to provide tactile sensations (and they work fantastically!). There are 36 speakers in total although the ones under the seat do not make sound - they just move the seats! My screen is DIY made from 1x4's and 1 layer of white over 1 layer of black spandex. It is a 2.40:1 scope screen. It is 124" wide (135" diagonal). Spandex makes the best acoustic material for a screen but it does have the drawback of being a bit on the darker side (not a great reflector) so you need a brighter projector to light up the screen. Good luck on your build!

Unfortunately the office in the bedroom is for my husband as he is currently working from home indefinitely and needs the privacy for phone calls and Zoom/Skype meetings. I was planning to have my desk somewhere in the main part of the house as I work at home occasionally, I still go in the office. Our house is 3 Bedrooms, Kitchen, small Casual Family Room in front of kitchen, and large open room (formal dining/living room) in the front entrance that is open concept. unfortunately there are no nooks, basement, or attics in the house which is why our space is limited. Each of the 3 bedrooms has a purpose: Master Bedroom that has limited space, Husbands office and he needs the privacy for phone calls, and the current guest room which will be utilized as a nursery/kids room in near future. The garage has both our cars already and we live in the desert where it gets over 100 degrees. So a gym in the garage is not an option.