You need that external autodiscover record yes if you want the ability for external clients to automatically setup and configure their mail profiles for all clients that can use it.
OWA doesnt use autodiscover.
If however , you are ok with users entering the mail.company.com IP manually, you dont absolutely need the autodiscover record.
Note, there is no need for a separate IP.
Use a CNAME instead that points to the mail.company.com A record.
Why the exchange.company.com IP address?