For question 1 the official answer is no you cannot use the same WD firmware on both devices due to each using slightly different hardware.
Unofficially it may be possible to somehow use the same non WD firmware but you’d have to search through the forum (magnifying glass icon upper right) to see if anyone else has done something similar. Also see user Fox_Exe’s Google Drive where there may be additional information.
https://drive.google.com/drive/folders/0B_6OlQ_H0PxVRXF4aFpYS2dzMEE
For question 2, again use the forum search feature. There are a number of past discussions on using rsync to copy data from one My Cloud to another or to a USB hard drive attached to the My Cloud. There is also a number of past discussions on using CRON to automate various tasks including rsync. When using rsync you can backup what ever you want on the My Cloud. Either the entire Share folder so you are backing up just the user data or one could try rsyncing the entire drive contents or one could backup select files or folders. The choice is yours.
While I don’t have two My Clouds, I do use rsync to backup several Shares to a USB drive attached to the My Cloud by way to a CRON job that runs every night and emails me when done. Made some comments on it in this thread/post.
