Powershell Create Office 365 Groups (unified) with assets

Yes, this is absolutely possible...bear in mind that you could find some challenges in regards of when the Group SPO Site is created, but technically you can just create a schedule task that check if the Group site is ready so documents are loaded in the document library...and yes, the right approach to do this is by means of the Graph. Take also a look at the possibilities provided by PnP n regards of provisioning modern team sites with a Group attached