Our Medium cushion moss terrariums come with their own grow light so they do not need any additional light. Keep the light on for 10 hours a day, make it easy by using a plug timer.
While there are small vents there is not much airflow so you wont need to water very often. Typically we only water our mini terrariums once a month with RO water (distilled also works). You may have mold issues, that is normal!! You can prevent mold by allowing your moss to dry out a little between waterings or having springtails.
Occasionally you may want to clean the glass, this can be done gently with a paper towel and tweezers. If you ever over water your terrarium you can gently tip it to the side and use a turkey baster to remove the excess water, the remaining water should not exceed the pumice layer.