Moving file and folders to mountpoint

Hello Forum, I need some help around a small project that I am involved with. For the sake of simplicity, I will use only one server as an example - this will give me conceptual understanding on how to proceed with the rest.

I have one Windows 2008 R2 server with file services installed, the server acts as file and folder server. It is in virtual environment with 5 virtual disks attached to it. One of the disks which is mounted as J:\ is running out of disk space and so I thought of adding one more disk to the server, mount it on J:\ and move files and folders. The folder I will be moving is J:\data\groups\repository. 

I understand that one cannot mount a filled folder, in other words it has to be empty. I have thought of a plan wherein I need inputs.

A. Stop sharing J:\data\groups\repository
B. Rename J:\data\groups\repository to J:\data\groups\repository_old
C. Create a folder J:\data\groups\repository
D. Add another virtual disk to the server
E. Mount the disk as folder using diskpart, exmaple diskpart assign=J:\data\groups\repository
F. Use Robocopy to move files and folders from J:\data\groups\repository_old to J:\data\groups\repository
G. Start sharing J:\data\groups\repository

I need help with step 5 and 6. Questions are:

Q. Is the diskpart command correct?
Q. How can I estimate the time it will take to move files and folders from old to new location?
Q. How can I preserve access rights and permissions on files and folders?
Q. Should I backup ACL from old folder and then restore to new?