Hi Sara,
As you are not sure of the number of renewals you can actually set the term type as perpetual (commonly known as evergreen), specify expiration date and set the appropriate notice period e.g. 60 (days) before you would like someone to get a notification to simply review the contract. Once you set the notice period to non "0" (Zero) value you will get the email notification for that contract before the set expiration date.
Hope this helps.
Regards
Vilas