Hi Dave, nice job mate. I cant wait to see pics when its done, I'm especially looking forward to seeing the glowing toilet flush button.
Grohe gear is top notch but damn expensive, worth the money though.
Is the bath mixer fed from unbalanced feeds? eg cold from mains and gravity hot, if so dont forget the non return valve on the hot to prevent cold entering the hot water system, which it will because of the higher cold pressure. It will push hot water back into the cylinder and back up into the loft tank and then pour out of the overflow. Granted it will only do this when your using hot and cold together, or if it develops an internal fault.
Many a young plumber has been caught out with that one, they keep replacing ballvalve washers but cant understand why the tank keeps filling!
Make sure you use the low pressure flap type or it will restrict the flow. Get them from BES Plumbing.
Plumbing Supplies | BES Gas & Plumbing Fittings Part 7463