What to send voters: the Staff ballot link only. Keep this index and the results board to the desk; the results board needs the admin key to show anything.
Embedding: the ballot is a full-width tool, so it works best opened as its own page. If you do put it in an iframe, use Preview to size it and Copy Embed picks up the height you set. Everything a voter does autosaves in their own browser either way.
Updating: upload a new zip to this same project any time; submitted ballots live in the Worker's storage and are not touched by a redeploy.