not sounding arrogant but as others have never built one before im mentioning another type of build
your explanation would sound feasable against flex and the strength needed for the cutting table surface and as explained there is outside factors involved with your build
I know its not a plasma or a welding table was mentioning those as they can be used the gantry steel within there tables and are replaceable but sometimes other builds can be used within other builds
Coming together now.
Shortened the middle bed rails to give me somewhere for the tool change rack. Changed the Gantry supports to be one piece items. I'm going to mill them from solid aluminium billet.