I'll try my best to answer.
Are there any library size limitations and if so, are you able to increase the size at additional cost?
If you mean for for the cloud library. Dropbox allows you to pick a larger storage option if needed.
I see OneDrive is used to sync files. Do the files your syncing have to be stored on a local drive or are network shares finally supported?
OneDrive is not used, only Dropbox at the moment.
The files will need to be sorted on the device they are synced to.
Are you able to stream media files your DJ'ing from the cloud instead of having to use a local copy?
You are able to stream media files through the streamings services like Soundcloud, Tidal, Beatsource directly. It will save cache of the file.
If you mean stream your own files directly from the cloud library, that is not possible. A copy has to be on the device in the Dropbox folder.
Will this work if you're already syncing files via OneDrive to Azure or a local server?
Cloud Library doesn't work with OneDrive. Not sure where you got that information from.