[lcstorc]

Add the LR in the beginning. First you will need to cure it. That is usually done in a tub of saltwater with a powerhead and heater. Test the parameters and do water changes as necessary to remove the detrius. Once the LR is cured put in in the tank with your water and sand. Add a piece of shrimp from the deli to start your cycle. Test your parameters until amonia and nitrite are gone. Then start doing water changes to bring down the nitrates.
I am not a fan of wet dry filters. They colonize the bacteria that is necessary for part of the cycle but leave the last step out which is converting the nitrates to a harmless gas. They are ok for FOWLR systems since fish can handle some nitrates. Corals and such cannot that is why we use the LR instead.
HTH