[Six-line Wrasse]

1 - 1.5lbs./gal. tends to be the faithful rule of thumb. I prefer .75lb./gal. if it's a reef tank since most rock will come with the coral and you don't want that overcrowded look that you're talking about.

3 - 4 fish is possible in a 20 Gal. They need to be small, low bio-load fish. I would check with this forum before adding fish.