[Al_from_Ottawa]

Still running Sierra because of compatibility concerns, especially MS Office 2011. Now about to try it. Need advice on best way to do it.

Macbook Pro 2012 with internal 1 TB SSD and available external 500 GB USB3 SSD. Full clone of internal drive will not quite fit in 500 GB. All HFS+ of course. There are some encrypted disk images, but neither drive is encrypted as a whole.

Here's my plan. But I am not sure it will work the way I hope.
- Sandbox clone from internal to external drive.
- Set boot to external then update to High Sierra. If I understand correctly, I will now be running High Sierra but all user file updates will still occur on the internal drive.
- If I want to revert to Sierra, I just have to switch back to booting on the internal drive.
- If I want to stay with High Sierra, I run the OS updater again on the internal drive.
- Either way I don't have to copy anything from the external to the internal drive.
- I would need to clone both drives to fully back up using SD.

1. Does this plan work?

2. What's the best way to handle Time Machine during the transition period? I have a pair of HFS+ encrypted 2TB USB3 drives used in alternation for Time Machine.

3. If I end up running High Sierra I will want to migrate to APFS. First step is probably to clone to an encrypted APFS drive with SD. Then what?