Seal up at tank shine a bright light on it you'll have a greenhouse effect. Also your tank still needs the exchange of air.
No sure what you're planning for ATO but
here's a simple gravity type.
If you are forced to go small, should skip the SPS (and the expensive lights). There's lots of really nice nanos out there with easier stocking and demands. Something as simple as a piece of LR, a mushroom and a shrimp can gorgeous if done properly, think bonsai.