Phil! You gona cut? Man - I'm gonna hope you keep working wire too!
Seems like you're be in the 48x36 inch range - xy surface. Probably want to keep that pretty rigid, so kinda big up and down stairs. Even 8020 gets to be a lug and a lot of tweak and setup if you disassemble too much.
How about hanging it on the wall downstairs and just taking gantry/bridge up the flight with the spindle and electronics? May be a compromise. Hang it from the ceiling?
Best of luck. Cheers - Jim
Experience is the BEST Teacher. Is that why it usually arrives in a shower of sparks, flash of light, loud bang, a cloud of smoke, AND -- a BILL to pay? You usually get it -- just after you need it.