Well for filteration i would remove all of the sponges and bio balls etc, as they will most likely harbour nitrates which is never good.
Your live rock will provide all the biological filteration you need, but you will need to provide water movement in order for the live rock to be effective. This is usually done by powerheads so you may choose to upgrade the pump in the tank to provide more water movement, aim for 20 - 30x turnover an hour.
If you have a built in refugium you can add live rock rubble/Chaetomorphia (will need lighting though)/phosphate removers etc. On my tank my back section has: Heater, temp probe for thermometer, live rock rubble in a bag (vaccumed weekly), a bag of RowaPhos and a bag of Purigen (for additional nitrate removal.
On a tank that size a bad skimmer will do more harm than good, and you really dont need it if you keep up with 10% weekly water changes.
If you intend on keeping corals you will probably need to upgrade your lighting, i would recommend a 70w metal halide lamp, these can either be store bought (expensive) or built from basic components, there are a few guides on this site somewhere. This will mean you wont have to worry about lighting issues for pretty much any coral in that tank.
Andy