Office 365 configuration and optimisation

I have office 365 which has been run by several people and I need it checking as there are errors on delivery, sending and configuration.

It mainly seems to be terrible on my iPhone for sending. I think there are two accounts set up and that the email is not properly configured with the domain.

I need someone to look at the whole account
Current setup and configuration.
Licences
setup user and sub accounts such sale@ Accounts@
Signatures


Also anything else that I am unaware of.

Also like some advise on Teams and its relevance to a small company compared to share point.

Would we benefit from SharePoint or teams?

How could we best utilise one drive?

Would we benefit from Azure?