I always rinsed the detritus out of any old sand being used in a transfer. Rinsed in tank water though, that was being used for a water change.
Again for live rock, rinse in old tank water and scrub any crap or algae off with a stiff brush. I use a tooth brush. An old one.
No other filters are needed with the sump. Skimmer & your reactors are all thats needed. You can run filter socks to catch detritus or clean it from the sump during water changes. Remember anything like rubble in a sump, will collect detritus. If running a fudge with rubble and/or sand, try have cleaner filtered water feeding the refugium. Its purpose is to provide hidey places and some natural food for the tank , not filtration.