I've done the same with NextCloud, host it locally in my office. But I always have asked myself "if the customer doesn't already have DropBox, Google Drive, or OneDrive, and they have to sign up for something new, what should that be?" I've been using Feng Office (https://www.fengoffice.com) as a customer collaboration site for some years now. It allows the customers to see tasks, documents, uploads, comments, etc, for a given product. With Feng, we have a central point of communication.
To the OP, if you want hosting for something like Feng Office, my company can host and manage that for you. You'll have full admin access, but we'll ensure the site stays up and running, and fast and secure too. (PM me if you want more info)
I tried to convinced my office to use FengOffice for documentation, but it never really caught on. Maybe you'll have better luck? The Community Edition (free as-in-beer) was plenty for just documentation.