Hello
I am an OS X system developer.
One of my previous projects was an add-in for Word 2008 for Mac. A customer already had a MS Word for Windows add-in, and needed a Mac OS X version. It was an auto-citation plugin, that dropped down a popup list of authors, when the user typed in special character, also converting these characters into a "field". When the user selected a specific author/book title in the list, the plugin inserted a field into a document, called it something like "[1]", and later inserted a citation to the end of the document. The plugin was quite sophisticated, it supported different citation styles (supplied as XML documents in a CSR format), etc.
Back then Microsoft didn't release publicly the SDK, so my add-in technically was a stand-alone application, that heavily used AppleScript to interact with Word. It listened for keypresses in Word, listened to events like "Word document's window has been shown/hidden", "document opened/closed", "caret moved", etc, and displayed a popup dropdown window.
What add-ins exactly do you need to have developed? Can I take a look at your existing O365 addins?
For what it's worth, I have created quite complicated macros using VBA back for Microsoft Excel and Microsoft Word. I do have experience with Visual Basic.