Hi Welcome.

Well your needs are small and they fit with each other well. This focused group of materials all need relatively high feed rates with the exception of PCB which needs high accuracy and low/medium feeds.(Don't do much PCB so not my strong point)

So starting with feeds then really you'll be better with RM1610 has they will offer good feed rates and resolution. Also if you connect motors to screws with belts then you have the option of gearing 2:1 and increasing resolution and torque for more demanding or resolution orientated work.
Your design suits having both screws being connected with timing belt which will work out cheaper and IME much better than slaved motors.

Your design could use a few small tweaks but it's very close. Size wise I'd maybe increase length to suit 1250 has sheet sizes tend to be 8x4 rather than 6x4. That said if you can live with 1000 then keep it shorter has it helps with screw whip at higher feeds.

#1 Add more supports for the base and cross brace to keep square and add strength.

#2 Gantry is a bit low and by time bed surface and then spoil board you won't have much clearance so I'd place some raiser blocks between bearing plate and gantry.

#3 Gantry sides don't need to extend past ballscrews and can go on inside of screws. This will put ball-nut mounts on outside and make alignment and setup bit easier, it will also make gantry and bearing plates narrower and that bit more ridged.

#4 Regards the rails then if you can stretch to profiled linear rails then do so has they are so much better than round and if you plan on doing high accuracy work like fine engraving or small PCB work they will pay dividends. If mostly wood work then round rail will be ok but they need more attention/maintenance and wear out much quicker.

Like I say small tweaks but quite beneficial to good machine.

Regards the Z axis then make it strong, use 20mm plate no less and Rm1605 ball-screw again connected to motor with a timing belt. Timing belts really help with resonance and make for smoother running motors plus they give flexibility of gearing if required.

Hope this helps.