my first tank never had a light, i just left a small gap in the curtains to let a little bit of light through.
Back to the cleaning, the point im trying to explain is that if you disturb the substrate too much the bacteria that are in there won't funcion very well and if something went wrong with feeding or if a fish died it would be far more worse than if you did a simple clean + water change.
If your going to use an auto feeder then you will probably need to use a flake or granular food designed to work with what ever feeder you use, so I would recommend you start feeding the fish with the food that they will have later when your on holiday and see if and how much of the food they eat and adjust the amounts accordingly.