If you plan on hiding your towers and subs behind a false wall, you just lost a minimum of 24" from the length of your room, maybe more. If you are planning on using acoustic treatments on the front and back walls, you'll lose even more. I think both of those options are worth doing, as long as you understand they eat up real estate and you plan accordingly.
Since you seem to have more speakers than you need, have you considered selling a few and getting yourself a nice set of in-wall speakers (Triad/Atlantic Technology). This will allow you to hold that false wall as tight as possible to the existing wall, freeing up more room for your seats.
If you are planning on using reclining seats, I would enlarge your riser from 5'-10" deep to 7' deep min. If you want the back row to be able to enjoy the rear surround speakers, I'd enlarge it to 8' deep. This will determine where your front row will be and will allow you to properly size your screen based on those seating positions. Assuming you can go with a shallow false wall and in-wall or on-wall speakers, eyeballs in your front row will end up approx. 9' from the screen while eyeballs in your back row end up around 15-1/2' back. If you decide to hide your existing towers instead of in-walls, your false wall will need to be deeper and those viewing distances will get smaller.
I think you already realized that sitting 9' from a 150" screen will be an unpleasant experience. My guess is you are going to find 120-130" too big as well, especially if you screen format is 16:9. Do you know what aspect ratio you want? Don't feel like you need to cram everything against the back wall so you can get a large screen. Moving the seats closer and getting a slightly smaller screen will give you the same experience PLUS it will make your rear surrounds sound better because you've put some space between them and the people sitting in the back row.
Keep in mind that most AT screens will have a visible weave when sitting in the 8-10' range. Something you should be aware of , especially if you build a deep false wall that pushes the screen even closer to the seats. There are some new 4K screens that are AT and will not have a visible weave. You might want to check them out
FYI-I have a similar sized space (depth-challenged) and opted to go with a very shallow false wall. My sub will sit behind my rear seats since I could not fit it up front.
What are your plans for dealing with the sliding door? Do you have a place set aside for your equipment?