I would consider putting the front sub behind the screen, but depends a lot on the look you want.
I ran both RG6 and 12 gauge speaker wire to my sub locations... I am currently using passive subs, with the Amp in my AV closet/room, so, using the 12 gauge speaker wire. However, I figured if I ever wanted active subs, with the amp built into the sub, I would want the RG-6 wire already there, so, I wired for both.
You have a nice size room! My front wall to back wall is about 23', screen wall to back wall is about 22'. My room is 17'6" wide. I squeezed in two theater seating rows & one bar row, but it is tight...with your extra room, that should be a nice lay out!