Migration question 316 and 516

I have a 516 up and running at the moment, and it's been running for over a year. It's set up as RAID6 with 3TB drives. I recently bought a 316 to back up the 516, and I also bought more drives. My thought is that it might be better to use the new drives in the 516, since that's what I access and use most times. I don't really want to have to re-configure everything from the ground up, but could if I needed to. I figure I have a couple of options.

1. Shut down the 516 and put all of the drives into the 316. It should start right up and continue on as my 516 did. This will become my backup. Then I can put in the new drives in the 516, set it up, and then just transfer the data back over. This is my first, and probably preferred idea. Does anyone see any problems with this?

2. Re-do all of the drives and restore from backups. This is less ideal as I have my backups on single drives around, and the cloud. It would take way too long to restore, and I don't like the risk of one of the single backup drives failing in the middle of the restore. 

Any other ways? Any problems with the first idea? I don't mind shuffling the data around, so maybe go with #1, then after transferring the data to the 516, factory reset the 316 and backup from the 516. 

I'm probably overthinking this...