That's what I am doing.
I plan a fish only 20 gallon but have been slowly adding live rock -- when I see nice pieces reasonably priced -- to supplement the filtration. So far, I have about 15 lbs of Live Rock and another 10 lbs of base rock that I can see is slowly being brought to life.
Yesterday I added a few crabs, snails and a star fish.
It will be a while yet before I add a fish.
With regard to powered filtration, I only have a an Aquaclear 150 with a couple of foam inserts and a supplementary power head. Lighting is insufficient for corals -- which I plan to leave for a while -- but will live rock be inadequate for a fowlr
The fish store hinted as much and directed me towards a small Emperor.
Am curious as to what others think. Jeff