“Serious” means nothing to me, And I can’t give specs since you will be building your own machine. See the FAQ’s for tolerances. In construction 1/32″ is ridiculously accurate, in engineering serious is a dimension followed by a temperature it is expected to be at while holding that dimension.
All my machines are about 24″ square with 3-6″ Z axis. I have a few aluminum videos.
I’m not saying it can’t be done 7′ could be easy I have no idea. If it is 12″ in the other direction I see no reason it won’t work. I will say 7’x7′ will not work.
So try it, make it 7′ by the absolute smallest you an in the other 2 directions. That is the point of this machine, make it your way. Just offering as much help as I can before you get frustrated.