I don't water any plants from below. Never understood the illogical mentality in doing so ... in the wild they get watered from above. (I have yet to see a plant in the wild whip out an umbrella to keep its leaves dry during a rainstorm.)

Most (perhaps all?) selags like to stay moist at all times. If your media is of a well draining kind, it will be difficult to over water. With some experience, the weight of the pot may tell you what you need to know -- provided the pot is a plastic one. Make a mental note of the pot's heaviness right after you have thoroughly watered it and have let it drain for 15min or so. Check by hefting the pot every few days. When it starts feeling fairly light weight, water again. Double check by sticking your finger or a dry dowel or chop stick into the soil about 1-2 inches down. If your finger/dowel/stick comes up dry, you need to water.

True mosses? Well depends on the type. Some do well constantly moist or even wet. Those from the cold climes often require a chilly to outright cold dormancy to remain vigorous.