I have a 5 gal fluval chi pico tank. I have live rock, pool filter sand, small HOB filter, thermometer, heater, lid for tank, 200gph pico circulation pump, a par38 bulb, and an API master test kit.
In my HOB I have live rock rubble instead of filter cartridges. I have a piece of filter pad to catch any larger debris.
I check my salinity everyday and top off with RO water.
I buy the petco natural seawater and it seems to be doing great.
Inhabitants: 1 emerald crab
2 nassarius snail
6 hermits (3 dwarf blue legs and 3 red legs)
Feather duster worms
2 cerith snails.
Zoanthids
Candy cane coral
My advice is to go slow. Read up on the nitrogen cycle if you haven't done so already. Since it is such a small water volume things can go wrong fast. Take your time and do your research and it should all turn out just fine. I've had my pico running since 8-22-12 (almost 3 months) and I haven't had any problems except for some hair algae. It's a fun hobby. Best of luck! I will be following along!