The thing with an unfiltered/uncycled large tank, such as a five gallon, is that they will require a 50% water change AND a 100% water change during the week in order to maintain water quality. That can make using sand irritating and expensive.
As for the snail, please note that snails are not just algae vacuums. They have their own special needs and do far better in cycled tanks. The most commonly sold snails are referred to as mystery snails by pet stores, which are actually apple snails. These snails tend to produce high amounts of ammonia because they leave waste often. An uncycled tank plus a high bioload from a snail alone sounds like a bad time.
Why do you not want to have a filter? I am just curious.