IP whitelist limit

Are you referring to RDS Security Groups? If yes, here are the limits (some are adjustable on request) - https://docs.aws.amazon.com/vpc/latest/userguide/amazon-vpc-limits.html

You could also look at using prefix lists - https://docs.aws.amazon.com/vpc/latest/userguide/managed-prefix-lists.html

Also, refer to prefix list quotas on the above shared VPC limits documentation.