Exchange 2016 Receive Connector - maximum number of IP's in the RemoteIPRanges field?

I do not have any documentation, but why not add another connector so you can add more IP addresses. Or try to make some authenticated connections instead so you don’t have to limit by IP address.

Another way is to restrict the IP’s with using a firewall rule instead, and just leave the Receive Connector open. But i think you can better go for the first option.