As mentioned the best way to get a good will stocked sand bed is to
trade a cup with others do it as often as you can find someone with a good healthy tank.
Maintaining a good sand bed takes a little work some thank the live rock will
seed it but you wont get the diversity you need from just your rock
Another good way is if you have a club you can all add a cup to a quarantine tank
and leave it for 6 weeks or so and divide it after