Hello Vee,
Good day and thank you for your question.
For throttling, to avoid it and for best practices, please refer to https://learn.microsoft.com/en-us/graph/throttling.
For the subscription lifetime, mostly, it is under 3 days (4,230 minutes). It is also noted that:
Note: Existing applications and new applications should not exceed the supported value. In the future, any requests to create or renew a subscription beyond the maximum value will fail.