Congradulations on getting to build an A/V room from the ground up. I can't help you with your room size, but I do know this, Now is time to get it together and plan on your electronics install. I built a house in Florida and had an A/V Company come in and wire my equipment closet, Zone 1, and Zone 2, those being the great room and master bedroom RIGHT AFTER the electricians. I used Niles everywhere I could, and even ran speakers in the garage! Yes we used the garage speakers quit often over the years.
I would have wired it myself, but I'm in a wheelchair and those days are gone. Anyways, everything but my speakers were hidden. I can't wait to do it again