It looks great. 1" pipe for the return is prefect size and 5/8 is good for your pump.You could loss two of the valves, the first one off the down spout and the second off the refegium and just use one where the skimmer is. Keep the one valve by the skimmer, like you have on your drawning. I plumbed mine the same way, but I put in unions after the valve on the over flow to be able to move the aqaurium or add one trick extras. Make sure to clean the pipes first and use lost of primer and glue. Rember to let the glue dry for a day or two. Good plumbing
