If you care thinking of a projector somewhere down the track, having the tv / screen on either of the 3.8m walls is really the only way to go. Your sofa may mostly block the sliding door to the patio area, but in reality, how often would you use it? If most of the family living is done in the dining / kitchen area, this is the area most likely to be used to access the patio, the family room may get opened up from time to time, but to have a bit of a tight squeeze to use this slider isn't a deal breaker in my opinion.

Your room then allows for a good 5.1.2 or 5.2.2 system, 3 speakers along wall with entrance,  ceiling speakers roughly where the couch is in your pic and two surrounds in back corners angled in. 1 or 2 subs along the front of the room. TV on the wall, drop down screen coming in over the top. Its pretty much exactly how my room will be set out in our new house, marginally wider than yours (4m vs 3.8) but marginally shorter (4.4m vs 4.6).

A 3m viewing distance will not give you immersion into a 55 or 65 inch TV, but you can comfortably fit a 106 inch screen at the front, this will put your viewing distance of around 3m very much in a good distance for immersion.