In the US at least, front doors and garage access doors are normally 36" wide, with interior doors being 32" wide. But you loose an inch or so due to the door frame and whatnot.
My driving cab (see signature) has a 32" screen, which is 32" wide.. so my cabinet is about 35" wide to "enclose" the screen. The entire "head" unit on my cabinet unbolts so I can turn it sideways to get through doors. I haven't had to do it since its in the garage, but its something I at least tried to plan for. And due to the size, its heavy, so the entire thing is on wheels. Saved my back at least a dozen times rolling the thing around.

For a triple screen setup (I've consider it many times), I think 25" - 28" screens should be ideal for me based on how far I sit back from the screens. The 24" screen on my desk is 23" wide - so more than triple that for bigger screens and then take off a little for the screen angles - and it gets really wide really quick. I'd guess at least 48" wide. Not something that'll fit through doors.