Large document libraries in SharePoint Online

Hi Heiko,

First off....I have no experience of Dynamics at the current time, so apologies if my points lead nowhere...

What I would do from SP side is use Content Organiser, with metadata and rules set by you - ideally you'll be able to set up and send the relevant metadata from Dynamics to SP (something I don't know if possible) - which you can use to send the documents to the correct list/library. Unique permissions as per your folder scenario above so the relevant permissions are granted to the correct users.

From a front end perspective (search/filtering) I would use AngularJS for such a large amount of data. In my previous point I mentioned using metadata, for your benefit for routing, not necessarily the end users benefit with their love of folders - you can style that how you please.

As Pieter suggested, I would also add on retention rules to either delete or archive 'old' data - if archived....again, I would AngularJS to make the archive searchable.