You should be able to get 300mm rails easily enough.
I usr 300mm for Y and Z and 350mm for X
Yes, provided that you can cut the steel that the rails are made of, you can cut them to length. You really should cut by 25mm increments (the holes are spaced 25mm apart) though you are by no means forced to. (I think the CAD expects it, so it might break in interesting ways if you try a different increment.)
In my plog, I listed the plastic pieces I printed. It basically comes to 1 each of the parts, with the following exceptions:
- 2 each of the Z motor mounts (plus the 1 mirrored Z motor mount)
- 2 each of the tension blocks
- 6 each of the Z belt holders.
I printed 2 of the rail alignment part which makes it a bit easier, but wasn’t necessary.