icml files and creating copies of indesign docs

I'm trying to understand why you would want to have two copies of the InDesign file and the .icml files. If I'm understanding you correctly, the duplicate InDesign file and it's .icml files will live in DropBox so that you can share it with a client. Will they be editing this InDesign file in InCopy? If they do, your local copy would be out of date as the .icml files on your local drive weren't the ones updated. Your client would update the .icml linked to the DropBox InDesign file. So you'd have to drag the .icml files from DropBox over to your local drive and overwrite those files.  Also, you mention that you exported all content as .icml files so you can add to the assignments when needed. However, when you export the content to .icml files, they automatically show up in the Assignement panel. Why would you need to add them to the Assignments panel again?

This all sounds exhausting and problematic to me. The potential for human error is giving me anxiety.

However, if that's the workflow you want, you can package your InDesign file and move it to DropBox. Packaging duplicates your InDesign file and all linked files which include .icml files. 

A simpler way would be for you to download and install the DropBox desktop app. That way files feel like they're on your local drive. Just work off of dropbox. No duplicates needed. Share the folder with your client who would also download and install the DropBox desktop app and access the files that way. No downloading/uploading of individual files. Once the project is done, revoke access to your file.

If the client won't be using incopy to edit, just send them a PDF, have them comment on the doc and send it back. You can continue to work on your local drive as was your original intent. Hope that helps!