We could refer to the official document which lists all the ports Exchange server needs
Network ports for clients and mail flow in Exchange
And Office Web Add-ins require a secure HTTP connection (i.e. HTTPS). Normally this would be handled over 443 but that is just the standard port. Which port you host it on however is entirely up to you.
Here is a related thread discussed the similar question: Can Office Add-Ins function if port 80 and 443 are blocked?
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