Did sb tell you already to rid of that ridiculous Y Hiwin design? Why would you need 2 rails each side? You need one rail and 2 blocks, size 20 which have 100 times the specs higher than your machine can weight or 10x force on them.

Before rendering the design, better think how you will mount all together. Especially how will adjust and fit things and with your design especially how you will square the Y rails/ yes again the Y rails./

While side mounting is very beautiful is very hard to mount them properly in DIY design, thats why people use epoxy and mount them horizontally. Or as per your design- all MUST be Machined on mill so you fit it right.

Same as front/back mounting ball screw supports.

So the way i see it- nothing wrong with all that if you are to mill all pieces on a mill/ not your old CNC/ . If not- the result will be mediocre concerning precision