Storage limit
I'm a new user and have just imported about 100 pdfs into my library, which doesn't seem like very much. But my account says that I'm exceeded my storage quota. I've merged duplicates and deleted the trash. I've also changed syncing to 'as needed'. Since doing this, my account has registered no difference in the quota used. I don't know what to do to proceed. Please help!
Your choices are to disable file sync, find a webDAV provider with more free storage and use that, or to pay for Zotero file storage.
Just to reiterate the _only_ functionality you pay for in Zotero is the ability to sync attachments to the Zotero server (and thus between devices). Regardless of the size of your library, you can sync item information ("metadata") between devices for free and you can use the local tool to manage references and create bibliographies.
Are you working on multiple devices? Is attachment sync important to your workflow?
On the other hand you can use the "attach link to file" feature and in this case the PDF can be anywhere on your computer, including your Dropbox storage. The upside is the PDFs are stored per your existing folder schema and you are limited only by the storage limit of your Dropbox account. The downside is that these PDFs will not show up in your online Zotero (because Zotero is not storing them for you). If you go this route, it is best to configure the storage location through the base file path option. I have been using this method for years and it has worked almost flawlessly for me. I have about 3000 PDFs.
It's fine if you're going to go that way -- that's why it's possible -- but gurdas is definitely a minority among power users to use the Dropbox set-up and that's for a reason.
Of course, I just double checked how much space I'm using and if I need to add more storage to my Zotero account... Good for now.