3 vs 4 bearings for y axis travel
Ideally you would use three bearings opposed to four. In principle you will only need 3 fixtures to get a stable reference frame. Look at how most Prusa i3 "X" carriages are constructed, they also have just three bearings.

Three bearings are way more easy to line out (especially with tight tolerance bearings), with four bearings you will get binding much more easy than with three.

I've been using three linear (self printed tight tolerance acetal/POM) bearings on the moving bed (Y direction) for quite some time on a Prusa i3 type of printer made from 2040 Aluminium profiles.



A similar reasoning applies to fixating the heated bed/glass slate, only three screws are necessary to define the reference plane. This is how my CoreXY heated bed is connected to the "Z" platform (a slate of glass is perfectly flat as a result of the production process).