Well, I think a lot of folks are going to focus on the theater aspects. Let me get those out of the way.
TVs above fireplaces are generally not a great idea. First, they tend to be too high. This leads to neck strain. You also need to tilt them down or you will get significant darkening of the picture. If the fireplace is actually used, the added heat will strain the TV and possibly cause early failure.
A corner placement is tough to get good sound from. Lots of reflections and very tough to get the back speakers into any sort of shape. If you are mostly a sports guy, I would suggest doing a sound bar and punt the surround. If you are looking at movies and TV viewing, you may want to rethink.
I'd consider moving the closets. They are taking up some of your best wall space, that near the fireplace.
A lot of the rest is personal taste. A long narrow space is well suited to being divided up into zones. Good candidates are a bar, a gaming area, a poker or pool table. It all depends on what you like. My brother in law keeps a couple of vintage Harleys there, but he is a bike guy through and through. Retired Harley engineer.
Definitely get flexible but comfortable seating if you do zones. Carpeting is dependent on what you plan to do. Soft and thick is good for theater, but indoor ouitdoor is better for a sports or kids oriented theme.