I'd personally not worry about projectors or ATMOS either. My lounge is 4.5m x 4.5m and there is no way it's big enough IMO for a projector. I have a 75" TV in there now and it feels like being at the movies. Due to room size, 5.1 is also more than enough to fill the room with sound. 2.7m stud is also a luxury that doesn't match the build IMO. Put that money into adding some more area to the house. Add draw wires to behind the hifi gear though, so that if you want to go ATMOS you can. Given you don't have the budget for many of the basics, don't spend it on things you may never use.