How long were you gone, Lights on for how long?
I would clean all the decorations (if any) and the glass and due a few water changes. Mag-Float makes a small magnet glass cleaner that would be small enough for your tank. As for a filter my prefrences are either Whisper or Aquaclear filters both are good filters. IMO
the Aquaclear is easier to maintain, but both will do a good job. Are you using any filter at this time?