Small tank is quite a difficult setup as the water parameters are often fluctuate alot in a day and cause stress to the reef inhabitants.
Temperature need not be too low. Below 23degC will condensate the glass outside. I put mine between 26-28degC.
Lighting is definitely necessary. Invest in good lights such as T5 or MH. Colour temperature is about 10K should be neutral. But still depend on what do you want to put in the tank and the appearance.
Make sure you cycle the water at least a month before putting any livestock.
Above all, pls read more on how to keep marine tank so that you can minimise startup failures, waste time, $$$, and eventually start to see your nick posting in the 'Pasar Malam'.