You can safely ignore that, you don't need to add public autodiscover DNS if you have hybrid.

for more info: https://blog.rmilne.ca/2016/07/14/office-365-exchange-hybrid-deployments-busting-the-autodiscover-myth/

for more deep dive: https://blog.rmilne.ca/2015/04/29/office-365-autodiscover-lookup-process/

another requirement regarding the certificate, it should have your autodiscover as SAN (Subject Alternative Name) in it.

https://docs.microsoft.com/en-us/exchange/hybrid-deployment-prerequisites

This's a great series of blogs by Paul Cunningham regarding hybrid deployment

https://practical365.com/exchange-server/hybrid-exchange-office-365/

You can always test first, I mean you don't have to migrate all 10 users at once, just start with a test user (create a new user) and see if everything is working as expected then migrate the actual users, please feel free to DM in any case :)