I would ignore resale at this point as its a trivial detail would be buyers wouldn't be looking at.

Focus on what you do for entertaining. Do you have people over often to watch a game? Do you have a large family that watches quite a few movies? If yes go 12.

If not go 8 and get more storage and game space.

To fit 8-12 people, don't skimp on the ventilation in the room.

The bigger the room, the more power you'll need to feed the speakers to hit the same sound pressure level (SPL) at the main seating position.

Use an acoustically transparent (AT) screen with three identical speakers behind it—this greatly improves your front sound stage.

Paint the room dark, including the ceiling. This improves picture contrast. Or better yet, cover the walls with AT fabric—this way you can hide speakers and acoustic room treatment.

Put shakers in your furniture—they're a cheap and fun addition to movies. Although as with anything, you can go overboard cost-wise with these as well.

Put the gear outside the room so you don't have distracting lights in the room. Plan for how you'll control the gear as well.

Plan for bass control. For example, a riser can double as a broadband absorber.

Look into Dolby Atmos—I did this in my last house with 7 identical speakers around the room and 4 overhead speakers. It was amazing.