Room is 21 x 14
Distance from screen 16'
Back wall 21'
Yes, I bet your mind is going nuts. Too little time to plan properly
You know the saying: you want it bad, you will get it bad.
That is a pretty long distance to watch video or listen to music. How large is the screen, if you are into movies?
That distance also affects speaker's capability and power needs for the speakers. It will need to play louder for a given level at the listening position compared to someone at 12ft, or less.
Speakers are what you hear, not the components, where most or a good bit of the budget needs to go.
If, all that distance is usable for movie and music, probably the 7.1 route is the way to go, at least in the planning and pre-wiring for speakers.