Changes apply immediately and are remembered for next time.
Shopkeeper markup, shop size, and rarity likelihood now live in the sidebar on the main page.
Saved to the server, shared across every device (asks for the site's edit password).
Shared across every device (asks for the site's edit password).
Everything's visible to players by default -- check "Hide" on anything not for sale yet, then Publish to push the current state to their page. Nothing changes for them until you click Publish.