snails, conchs and crabs as wel as pods and worms are the best thing for a dsb, you(as mentioned) only wat to disturb the top layer, the lower layer you want to remain unchurned, the worms will work it good enough. The idea is to have a stagnant oxyugen deprived area of the bed, this is where bacterias live that do more for reducing nitrates than many pieces of equipment can do effectively.
as for the stars and cukes, 1 was already mentioned, the cukes have been known to dameage tanks, if they get stressed. The stars sift the sand, while eating the pids and other fauna in your sand, whihc you want to keep.