Ok 12.5mm plate is too thin you need 19-20mm minimum other wise it will flex, you could get away with 12.5 on the rear plate but I wouldn't advise.

The way you have the ballnut on top of front plate means the rear plate is longer than needed really wasting money and adding weight.
The screw not being supported at both ends isn't a problem at short length(<150mm travel) but if having long travel and with you having ballnut right at top then supporting both ends would be better.

Bearings are too close together which has been said. . . . BUT .. . Also you haven't shown how it's fastening to Y axis carriages and I suspect those bottom bearings will be in the way of bolt holes.? It's a common Err and chances are you'll raise them up 20mm or so.?

I wouldn't get too carried away with trying to reduce overhang, the little you'll save won't make a big differance to cutting area but could to performance and quality of cut if taken too far.!!