Do I need a permit for sheds, above-ground pools, lean-to's, etc.?

Yes.  Kingston requires that all structures be permitted.  One of the main reasons for this is that the Building Inspector is expected to ensure that the mandatory set-backs are met, but he also must make sure that all structures are safe and that, if they are taxable, the town has a record of them.  Unpermitted structures may have to be removed if they fail to meet setbacks or if the Building Inspector determines that they were not built according to code.  Building or locating of structures without a permit is considered to be a violation, subject to enforcement by the Board of Selectmen.