I had the same questions and came to the conclusion that you need to keep a couple fish in it to keep the bio filter going. For bio filter, get one of the hang on tank filters with a bio grate or bio-wheel in it. Put some shells or dead rocks in for hidy places but keep the decorating "minimalistic." (Less to move when you need to catch someone.) If it will also be a hospital tank don't add live rock or sand because you will kill them the first time you have to medicate.
I do water changes, check ammonia, nitrites and nitrates and vacuum the same as with the big tank.