I can’t say for certain, but I think you could build a frame that would work with 5x5 ply… You’d want to build it 5 x something bigger than 5 … like 8 
in order for the router sled to have something support it when its working at the side of your piece. I don’t know if you have to do anything special to get it to work (other than calibrate it correctly).
check out this thread regarding other concerns (still seek verification about 5-foot height)
https://forums.maslowcnc.com/t/realistic-expectations-of-the-maslow-cnc/1368/3