splendid, this is where drawings start to earn their keep...
if you are hoping to use nuts on those rails it may pay to have the long box sections open instead of the short ones like you have drawn
it will still be a pain to get nuts in but not impossible :)

run the rails all the way to the back of your frame in light of the fact that your Z axis is likely to have an overhang that will push your cutting aria forward too the inside of the aperture of your frame

you may need to extend the frame to keep the Z inside the frame at its furthest reach… easy enough to amend as the drawing develops :)