The setup is feasible with the exception that I would recommend getting one Xpro-N Trigger instead of 2 Xpro-C (C is Canon, N is Nikon).

You do not write the size of the softboxes, I would recommend rather getting one 120cm round or octa and two strip boxes. With softboxes: the larger the softbox relative to the subject, the softer the light. If you have the room, bigger tends to be more versatile. 

The SK400 works with the Godox Xpro, no coupling is needed. Just the correct channel and group.

If you get the walimex background system with levers instead of wing-nut-like fasteners, you will notice that they become lose with use. A small tip would be get a cheap pack of manfrotto plastic cable clips. They, by sheer coincidience, have a side that is the right-sized key for refastening the levers.

I would also recommend getting some cheap sandbags, as a big softbox tends to need some counter-weight with the cheap and light lightstands.