What's the 'ideal' room size?

hi guys and gals,

I just bought a house and it's got a good size space in the basebament about 16'-8" X 18'-4" that I'll turn it into a movie/music room.

I can make this room smaller as I refinish the etire basement.

So I'm wondering what's the good size for Movie/Music room?

I'm thinking about 60" TV with either Kef Q5 or B&W DM603 as main speakers and a 12" subwoofer.

Thank all you experts out there.