Yes. I'm sure that Certsage will be getting an update at some point in order to explain things a little clearer. All Certsage is doing is sending the email address to the Certificate Authority (the CA, Let's Encrypt in this case), but the CA can choose what it wants to do with it. And the CA wants to (in order to help protect your privacy) no longer hold the data of which domain names are associated with which email addresses.
The first time with a new account, Let's Encrypt is planning on sending an introduction email with information on how to subscribe to their general-announcement email lists, but yes in general it won't matter if you put an email in there or not, especially for renewals.
Yes, you should all along be monitoring your system and ensuring renewals happen rather than relying on Let's Encrypt's reminder emails. I would actually recommend an appointment every two months on your calendar if you need to renew manually, just to ensure that you have time to deal with problems or vacations or whatever. You may also want to upgrade to the latest version of Certsage, which tries to renew your certificates automatically. (Though adding one of the external monitoring solutions that Let's Encrypt recommends as a replacement for their emails might not be a bad idea too.)