Looks like you have a good start to your room. As to screen AR and size, those are somewhat personal but I can tell you what I think based on maybe what most people would like or what I would like. In a commercial scope theater doing CIH presentation most people fall into a seating distance of between 2x and 3x the screen height, where the average viewer would want to sit about 2.5x the screen height.
Home theater is a little bit different because our PQ now with 4k projectors and our perfect blacked out rooms and mostly the fact that at home we watch many more movies per week and start getting used to the immersion and my guess is 90% of the people that start out at 2.5x wish they had gone some larger within the first 6 months. Another contributing factor is with two row seating at home the second row quickly becomes way under immersive like sitting in the back row of a commercial theater or even more.
As an example in your room if your screen was almost the width of the room 154x64 or 167 2.39:1 screen and you take your front row distance 129/64= 2.01x SH seating distance. That would be just about perfect for me. now 210/64=3.28x SH seating distance and that would be kind of like sitting pretty far back in a commercial theater. You can see if you desire say 2.5x for the front row the back row will get even worse.
So for those reasons some people start a little closer than they might first think.
Another problem is if both rows recline and a 12” riser making sure the screen height is high enough for the back row to see over the heads in front without making the screen overly high for the front row.
As to screen color and material if your room will have no outside light coming in and will be treated walls, ceiling and floors with dark light absorbing materials a simple 1.0 gain white screen would be best.
If you go with a screen as large as the width of the room it will be very important that the side wall be very dark even black velvet for at least 6’.
Having a screen that large now leaves you no room for speakers so a false wall would be needed and then place the speakers behind an AT acoustical transparent screen material. Doing that will shorten your throw distance and also your viewing distance and allow for a smaller screen size accordingly.
Hope this helps a little.