You need to debounce your requests to your endpoint. You cannot hit any API so many times without waiting on the results and moving on to the next one. In a sense you either queue your calls from the frontend or on the backend, that isn’t something I think CoCart should handle. If you are using javascript you can await each API call. Alternatively you can debounce the requests (more info here).
Why would this not be possible with a slug? You may not have access to the ID all the time?
Likewise. Does not change category. Saw on another thread that I may need to allow cron jobs on from within my config file. Can you confirm?