Check with the city and the builder. Some prefabs are considered manufactured homes and that's not allowed in Edgewater- you can't have a stick built and a manufactured on the same lot.

You will need a site plan plus a survey, permanent foundation, and permanent utilities. I would advise having separate utilities for the ADU. If you rent it down the road, it makes it easier to keep it separated for accounting and rental disputes. It also increases resale value.