how can you have a 500mm bed with a 381mm (15inch) centre ?

Other than that, sounds good.
But the printer itself isn't that large - so not sure why you want nema 23 motors.

The best thing to look at - as far as measurements go - for a delta is the smoothie ware, guide and wiki. Gives you all the rod measurements and angles, etc.
Reall helpful.
I presume the skyr 1.3 runs smoothieware ?