Institutional storage subscriptions

If you're at a university or college, check with your librarians to see if they've paid for an institutional storage subscription. I'm a librarian at a reasonably large university and the cost for adding unlimited storage for every user at the university was very reasonable (and helps support the project). Removing concerns about the 300mb storage sync limit really helps with adoption.

If that's not an option, then you can synchronize just metadata (including annotations that you've made on PDFs with Zotero's built-in reader). 300mb of metadata is virtually limitless. Or you can pay a small annual fee for plenty of personal storage, which I did for years until our institutional subscription began.

The server API is also quite powerful. I created and ran a searchable database with over 10,000 citations for years that synced it's content from a Zotero collection that we made publicly available. I'm now using https://github.com/whiskyechobravo/kerko for the same purpose instead of my custom code and am very happy with the results.