For those 40 x 60 frames be sure to calculate the weight of the plex and masonite and artwork, and only then select a type of frame and mounting scheme.
Also, be sure to evaluate the weight trade offs for different thicknesses and types of plex, balanced against your estimate of a tolerable amount of funhouse-mirror-like reflections from warping. If you want to use anti-reflection plex, evaluate its visual effects when placed at different distances from the artwork surface.
Defer making your bulk materials purchases until after you have assembled a single prototype, which will help you understand many things including the problems associated with plex that is pinched even slightly by whatever is supporting it, and problems with flexure in the overall package, and issues with your hanging scheme including inadequate bracing. And a lot more. Be sure to evaluate the prototype in your intended installation location with all the lights turned on. And while there, consider whether or not a plex cover and a masonite backing were good concepts to begin with.
If that seems too much, then hire a framer which will be cheaper than getting your fanny wupped by newby mistakes made several times over.