Are we able to support TLS certificates with a validity over 3 years?
With Let's Encrypt, the certificates have a validity of 90 days.
With Symantec, the certificates have a validity of 1 year.
It is possible to support certificates with a longer validity by using the third-party certificate option. With this you can use your CA and get a certificate issued with a longer validity. There are certificates deployed with 5 year validity.