New CNC Router Build I Designed

Evening All.

I'm not new to machining, but have been out of it for a long time.
From school I served an apprenticeship in a small machine shop where we designed and built machines for the likes of Loctite, Proctor & Gamble, centred around tube filling machines back then. to name a few so gained a lot of experience with manually operated lathes, mills, grinders etc and then basic CNC programming on the companies converted Bridgeport vertical mill. I was the youngest there so picked up the CAD to machine side quicker.
Anyway I have delved back into engineering to some degree with a laser cutter and more recent 6040 Chinese cnc machine with my own home built DDCSV1.1 standalone controller build driving it nicely once I replaced the lousy TB6600 drivers :-)
Now while the 6040 works ok, as we know it's not the most rigid and so with my CAD skills I have been designing a new frame centred around the use of aluminium extrusion, in thsi case the 80 x 160 and 80 x 120mm sized stuff, with 20mm Z axis vertical plates and maybe 15 ~ 20mm end plates for the extrusions.
From what I have seen and learnt in my travels on thsi forum, thank to all those who share their knowledge and experiences, I think the design isn't too bad. It's seriously over-engineered I think, but I am one of those that feels if I am going to do something I will do it right the first time and not wish I had of done so later down the line.

I have attached some images of the planned layout, I appologise up front for some of the colours used making them difficult to see. But from my former engineering days I've not bothered with producing fancy looking 3D drawings, just the usual 2D projection type to build from.
I've started to gather the parts already, the extrusions came from China and their cost is being recovered as they have been dropped and bent out of shape on the ends so are of no use to me. Will then re-order from a UK supplier.
For linears rails, I am planning 20mm on the Y axis and a pair of 25mm per side of the X axis with the ball screw running between them. This is where the overkill is I think from what I have seen, but atleast it won't flex :-)
Z axis, not really got that far yet. Thinking to build the main frame and then look at the Z axis as it starts to come together.

However I have some questions and may well have more in time I would like some advice on please.

1. I have used twin ball screws on the X axis, originally being driven by seperate belted Nema 23 steppers. However I am now wondering if a single Nema 34 mounted centrally with a longer belt linking both ball screws will be better still? Was then thinking to fit a single closed loop stepper as well. So would two steppers, one per ball screw be better than a single centrally mounted one with longer belt linking the two?

2. I have Z shaped the vertical Z axis standup plates as much as I dare currently, is there a limit as to how much you can do this reliably?
The centre line fo the spindle is then not far off the middle of the linear rail blocks, thinking about minimising the twisting/levering forces here as much as possible. Also material costs, the further the offset is the bigger the rectangular pieces of aluminium plate will need to be to achieve the shape.

I'm sure there is more questions, but that's all I can think of for now.
Any and all comments welcome on what you see in this design.

Thanks.

Ian Contessa