Please guide on number of "Recycling when the maximum number of requests is reached" what should be number here?
Recycling when the maximum number of requests is reached - it is recommended to set this to Unlimited. When the threshold is reached, the application pool is recycled, and all the session data would be lost. By default, IIS application pools recycles at a regular interval if there are no requests. It is also possible to put a threshold on the total memory used by the application to trigger recycling. You may check How to limit IIS worker process memory consumption on Plesk server? – Plesk Help Center