You need an active plan to generate an API key. Keys stop working if the subscription lapses — you'll get a "subscription inactive" message rather than a broken-key error.
Technically yes, but don't. Allowances are per account, not per store, so both stores draw from the same pool and revoking a key breaks both.
No. Every generation is a draft you review and accept. There is no unattended mode.
Generation stops for that module and the error names which allowance ran out. The others keep working — alt text, product listings and content have separate allowances.
Generations are stored in your ShopAltAI account and appear in the listing pages there, whether created through a plugin or the web app.