Originally Posted by Maschined
Is it worth taking measurements with REW to get a rough idea of the best place for a listening position now
I probably wouldn't bother.
We are thinking of having low storage down one side of the wall (low enough to allow 1st reflection absorbers to be mounted above it). Will these unbalance the sound at the listening position, do we need to keep things symmetrical?
Since you're building from scratch, I'd split the storage to be half on the left and half on the right, along the center-rear parts of the side walls to avoid blocking the front and rear corners where bass traps will go.
You definitely don't want your seat halfway back in the room as shown. If you plan for about 38 percent of the way back, you'll be close to your final place. More here: How to set up a room
I'll leave your remaining questions for others to answer.
--Ethan The Acoustic Treatment Experts