Was about to get a toy- then I did some research...

[Juranovich]

It does not matter as far as you use Hiwin 20 size or comparable rails.

20mm is the plan, but not sure yet about going full hiwin or not...

If it helps I use 300mm wide plates with this design.! Anywhere between 250 and 300 will work ok.

The idea crossed my mind. Would help bring the cog slightly forward + more stability.

I could also get creative and hang a 5kg weight from the spindle :D that should balance it up!