I’m in the processing of purchasing a piece of Acrylic.  But I’m not sure of the correct thickness.  I want to get a way with the thinness possible sheet, because of cost.  But I’m afraid that something around 3/8” might flex too much.  Or should I just go with a 1/2” or greater at my desired size.

Also, with a surface area of 48 X 36, will my SFH485 leds be bright enough at one inch a part.  Can I get away with two inches for my 48” x 36” sheet of acrylic?

Thanks in advance

I’m not one of the “experts” here but I work with plex-glass and know that a sheet 4’ x 3’ x 1/2” will flex if its horizontal.
You may have to go thicker ( 3/4” + ) = $$$, if its horizontal, and a smaller area to maintain a level surface. Also dragging or touching a larger screen puts pressure on the surface which could concave it slightly.
A sturdy perimeter frame, supported, will help a bit. Vertically theres not pressure on the plexi until you push on it.

Just a note: If your whole table is enclosed, with all the components inside, they may create enough heat to offset droopage over time that will occur. The plexi will expand minutely on the warm side while in use. I’ve seen this happen frequently with no ill effects.