I went through this same process a year ago with my portable lowrider.
Your rails need to be perfectly parallell to each other. This is easy for the xy axis using stringers between the rails. It’s a bit trickier in the Z because of unlike a fixed table that can be shimmed level, your floor surface is probably not fefectly flat.
My solution was to create a flat plane by using 2 sawhorses. I level each independently left and right but don’t worry about the slope between them. This gives me a planer surface that I can tweak if needed. My lowrider actually goes about .5 inches inch uphill over the full workpiece as my garage floor is sloped.
The centipede is going to give you too many points in space that aren’t planer but instead a mesh projection of your floor. You are going to find that you want to attach to only 4 attachment points to get to get a plane and that the centipede isn’t designed for point loads like that.
Also keep in mind that if you want a full 4ft cut your table needs to be almost 5ft wide so you will need to cantalever your load past the edges of your centipede.
Sry for the negativity just trying to point out some potential potholes that you may not have seen coming. My table consumed my mind for almost a month so I know how you’ve got a million ideas floating around your head right now.
Good luck on your build!