Are there any other additional costs with the rekordbox subscription charge?

You'll need to subscribe to a Dropbox plan to save your files if the total amount of the files you're uploading via Cloud Library Sync exceeds the storage capacity of the Dropbox Basic plan. We recommend subscribing to a paid plan so you can upload more tracks to the cloud.

For Professional plan users:

You will not need to sign up to Dropbox separately, as unlimited Dropbox storage capacity is included in the plan price.

For streaming services:

You'll need to sign up for each streaming service separately, regardless of which rekordbox subscription plan you use.