Hi mate,
Im currently in the same process, I'm going the fish and live rock only route.
I have taken everything out my tank, you obviously cant keep the plants, rock or bogwood. You can keep the pumps (need around 2) heater (need 2) one for the tank and one to heat up the water change bucket, you can also keep the tank (if its in a good condition) and also the thermometer.
I had a jewel tank and ripped out the heater section, this is where the filter pads where as these aren't required as live rock does this for you (also a bonus as it gives you more space.
Other than that if your going the same route as me I beleive a hydrometer, salt, ro unit, coral sand and another thermometer (for your mixing bucket) to be it. Oh and also a blue tube to give the fish a better viewing light.
If your going the coral route then expect to pay lots more and require ALOT more.
I think thats correct as im also new to marine.