I would let it cure overnight before running water through it.
Also, for choosing your pump you will want to determine your head height (will be roughly the distance from the pump location to the top of the tank). Then find the pump flow curve for the pump you are looking at and match the head to the flow desired. You can always restrict the flow using a ball valve, which essentially just increases the head.
For example I run a quiet one 2200 rated for 581gph on my 55gal. My head height is around 3.7ft which will give me just over 400gph at max flow using the pump curve shown below: