I like #3. What about a group of Dwarf Sunfish (of the Elassoma Species), and some native Killies? They are interesting little fish, require no heaters, minimal lighting, and minimal flow. Only drawback I've experienced is it can be a bit difficult to get them to accept foods other than live.
I do really want to try pygmy sunnies but I wanted do a trio in something a bit smaller (10-15 gallons). Good suggestion though, I'll consider it though!