You can safely delete the Outlook Pref file. Your account information is logged in Keychain Access, and Outlook's fonts are embedded within the app itself. You may need to re-authenticate your email account passwords if they include two-factor authentication.
You did not offer whether Outlook 2016 is part of a stand-alone suite or Office 365; if it is the latter, you may be asked for your O365 credentials.
I'm having an odd issue where messages get converted to Times font when viewed on mobile (iPhone). Is there some file I could try deleting that might fix this? I tried the MicrosoftRegistrationDB.reg file but it didn't work.