I understand that everyone wants to build it big, just in case, but your are starting at the very extreme of the machine. If you have no CNC experience your are making it extremely hard on yourself to learn. Your CAM skills will have to be exact for it to work at that size, I mean perfect.
You really really should build it much smaller and learn it.
I can’t imagine you will use a 6′ finger joint very often. I have a construction background and I think the biggest I ever used was about 5″ “and that was large) for drawers.
I am not trying to discourage you but conduit is a few dollars. Build it small and learn how to use it, then if your really need to try and scale it up and see what happens.
I am in the middle of building a large format machine but it is slow going do to holiday sales.