Looks like it worked out for the better. I probably would have returned the fittings as well which would have been the right thing to do. They might charge you for that if they inspect the package.
Either way, the pump's RGB is compatible with Asus's RGB which tells me the wiring is the same and as we can see in the image it worked out nicely.
The problem with the pump speed could be of two things. The PWM signal from the GPU is too weak therefore by default, these pumps run at irrc either 60% or 100% when there's no PWM signal by default or the header on the GPU isn't PWM at all or needs to be enabled via software, again not sure.
The radiator you picked is 19 FPI as opposed to the 8/9 FPI rads for low speed fans and low noise. I would recommend not going lower than 1200 RPM on this rad or at least find the sweet spot you're comfortable with via temps and audibles.
Whatever you do down the road, you got a really nice D5 pump in your hands that should last a while as they are one of the premium pumps in the market place and this particular one from EK has 15% more performance than your standard D5 pump.
For fluids and tubing, I would recommend EK's clear premix fluid or Aquacomputer's clear DP Ultra with a annual drain and refill, don't forget to add a drain port at the lowest point of the loop or just outside the reservoir via T-line of some sort to make your life easier when draining during maintenance, and for your tubing I highly recommend the PrimoChill Advanced LRT and the choice of color since you're better off staying away from color fluids.