agreed. A small system is going to require more care on your part, but it can and has been done. Patience is also a requirment, but with a little time and effort, and you can a have a very nice nano.
The small PCs are perfect for a tank 20 gallons or less. Id preffer T5s but go figure, they dont make them for any tanks less then 24 inchs in lenght. about 8 lbs of LR in the 5G would be fine, and about 15 lbs of Live sand, should be more then plenty.
I would strongly consider a way to purchase RO water for this tank, because the smaller the tank, the better the water is going to have to be. Filtering is harder, Skimming wise because most skimmers designed for nanos, are not the most efficient things you can spend your money on.
around 4-6 weeks for a cycle and get some coral in there, and you basically have a finished tank. As mentioned, a 5G tank, is not suitable for fish. If you were interested in fish, the only ones that would be okay in a smaller setup would be clown gobies and watchman gobies. Shrimp will also work, and if i dont say so myself, a good one to start with would be the fire shirmp, AKA emperor shrimp.
good luck, and remember, take your time, and research anything and everything.