Yes you should water cool the gpu if you are able to.
Everything runs cooler.
Adding a gpu to the water loop won't change the overall temp much you will reach delta faster tho but most will never notice a difference.
Will be a beast when 30XX come out.
I canceled my order on newegg for a psu recently because it had been 30+ days backorder already.
That psu will work fine for 30XX I would hope anyway they do seem to be power hungry but we will see.
I seen that the other day but have always wondered about that because my brother has an aio and you can hear the air gap in it.
He has the rad mounted at the same height as the pump. Everything is working as it should so far.