Do the boring parts first
Sound isolation, wiring and seating geometry are all effectively impossible to add later. Insulation in the walls and ceiling, a solid-core door with a seal, conduit to the screen wall and the equipment location, and dedicated circuits. Screen size and seating distance decide the room layout, not the other way round.
Light control
In Florida a room with a window facing the pool is a difficult theatre. Full blackout or an interior room. Recessed lighting on a dimmer, and nothing that reflects on the screen.
What a home theater room in Orlando costs to get wrong
Retrofitting the parts that had to go in while the walls were open. Isolation, conduit and dedicated circuits are cheap during a build and expensive afterwards, because adding them later means opening finished surfaces again. The other common error is buying the screen first and discovering the room cannot support the viewing distance it needs.
What a home theater room cannot add later
Isolation, conduit and seating geometry. Insulation in the walls and ceiling, a sealed solid-core door, conduit to the screen wall and the equipment position, and dedicated circuits all have to go in while the room is open. Screen size and viewing distance set the layout, so they are decided before anything is bought rather than after the seating is in.
Heat
A closed room full of equipment and people needs its own cooling and a ventilated equipment location. A rack in a sealed cupboard is how amplifiers die.