SharePoint and Teams: Better Together

Hi All, i would appreciate some practical guidance. I'm not an MCSE but am responsible for IT in the small business i have just joined. I would like to move the business onto the 365 platform, away from gsuite and Dropbox for all the reasons you understand. My challenge is to figure out how to align my classic view of the world (the shared drive with folder per division and access control ensuring that you only could access what you were allowed to. This world of course was never shared with outsiders. So on the one hand, I'm thinking of using SharePoint as i can easily align it with the "old world" that i'm used to and that also easy to explain to my colleagues and also ties up with how they operate sharing files a drop box folder. I also like SharePoint as it give me (as admin) the ability to share our world with outsiders - as a small business we outsource a lot. So things brings us to Team - clearly teams is the way to go but ... how to i reconcile the need to have a sensible data data structure that i can audit, secure, backup, version control and selectively share with outsiders (my love of all things SharePoint) with Teams that seem great for collaboration and day to day work in and across functional areas but runs the risk of becoming a squirrels nest and when the auditors come to call potentially very difficult to demonstrate that documented process and practice are aligned. I want structure and informality - my consultants say Team and I say "classic" surfaced by Teams. The approach i am consider is this: 1) Setup the core structure of each business (we operate 5): /Business A: /Functional unit 1 /Functional unit 2 //Functional unit ..n 2) Create Teams: 2A) Team - the Operators / setup a channel for every functional unit and surface each of the functional units as a SharePoint link into the channel My logic, we can have a helicopter view over all the folders, add conversational pieces around and work in the Team but when we "commit" a file, project etc, it will be written back to the formal persistent data structure - 2B) Team - Fund Admin This Team would have its access restricted to the "Fund Admin" folder - and in my example would be shared by the "Operators"and the "Fund Admin" Group, who are external. The logic is to provide a shared space with the administrators, where they would work solely in the Fund Admin Team space while we, as the "Operators", would have the option access those same files via the Team - Fund Admin or the folder through the Fund Admin channel in the Operators team. Teams will come and go and team sites will need spring cleaning from time to time - mission critical data should never be lost in the event that a team is deleted or over-zealously cleaned. Your guidance and philosophy will be greatly appreciated.