25 gallon setup

Hello, I've kept freshwater fish for many years but I've decided to give marine a go. I've got a spare 25 gallon tank and a fluval u2 filter ready to go. Would I be okay to use this filter if I change the elements inside to new ones? I'm also planning on getting 2 koralia nano pumps, or would just the one be sufficient? I'll also be getting love sand and live rock and will then be giving it time to cycle. Would this size tank be sufficient for a pair of clowns and damsals and maybe a goby? Or would this be over stocking?
Any advice would be much appreciated.
From an aspiring reefer