Can the Mini Silver Kit be used more than once for multiple small pieces, what is the shelf life if so?

The Mini Silver Kit covers 8 square feet so you can use certainly use it for multiple small pieces that add up to that coverage. The Tin for Silver is best stored in a freezer and the Pouring Silver chemicals in a fridge. If you do so the Tin will have a shelf life of approximately six months and the Silver Solutions have a shelf life of a year. The other products will extend beyond a year.