Setting up a 2 channel listening room

Looking to create a decent listening room. I have a media room that is being built in my new house, nothing too fancy. It is a hair under 18x14 feet, long side is free of windows, the room is symmetric and the ceiling is angled from front to back (9ft rear ceiling, 8ft front ceiling).

I am having them place a dedicated 20amp wall socket at the front end.

I am also thinking of having them double up on the subfloor and possibly having them encapsulate the entire room.

After this I was thinking of buying some audio/bass traps and playing with them.

Any other thoughts on setting up a good 2 channel room?
I would furnish the room first, carpets and such, set up my gear and listening position and just listen how it sounds. Only then I would consider how to deal with side wall reflections and standing waves. You could of course also use some form of DSP first as a rough guide and then tweak room, gear and listening position to your liking.
I had an echo at the front wall - I managed to eliminate this by placeing a couple of fabric panels 15 inches wide from floor to ceiling (almost) on the side walls at the corners that were slightly angled.

Once all the furniture/components are in place as Detlof says, walk about the room clapping - If you hear an echo then you'll need some form of treatment, like wall panels/ drapes, to eliminate it.

Eliminating the echo resulted in a less confused image

Be careful of overtreatment - it can lead to a dead and lifeless sound

Maybe get them to install 2 by 4 gang 20amp outlets instead of just the one. Also consider adding outlets where you might add monoblocs.
Bass traps and/or quality room correcting preamp for bass issues. Using bass traps is probably the best option. For other issues, I prefer diffusion rather than absorption for the reason Willy just gave.