A DSB in a 5g will take up lots of room... Just a thought.
You can get as fancy or stay as basic as you want. My 6g currently has no mechanical filtration, no DSB, no sump, no fuge, no skimmer, no nothing... except I left the bio-wheel in place. But without these other forms of filtration I'm relying on water changes to keep the nitrates down. Currently I'm doing 1g per-week water change. I'm dieing to add a fuge, which I plan to do so soon. I'm thinking around a 10g fuge.
No fish in a 5g I would think but maybe some decorator shrimp.
A 32w PC would be nice if you have room. You could keep most any softies with that. LPS too if there is room.
HTH,