In a Macbook, I'm ready to change the boot disk and replace the superdrive with an SSD. How will Migration Asst work? Use APFS?

Question

In a mid-2012 MacBook running Catalina, I'm first going to replace the DVD SuperDrive with an SSD. Boot-up and then make sure the drive is recognized and wifi, Bluetooth, camera, etc. still work. ok.

Next, I want to replace the current drive with an SSD. However, I've looked over Migration Assistant and I don't understand my best option. Here is situation:

1. each of the new internal drives are 1-tb Samsung 860 EVO and will be formatted APFS.
2. the current drive is a 250-gb Samsung 840 EVO with 80-gb free space and is formatted APFS.
3. a TmeMachine back-up exists on an external usb-drive formatted HFS+.

note: I have an external monitor connected via USB. The Catalina upgrade required some difficult security configuration to get it to work again and I don't want to redo this. I've also got a mysql database that I don't want to reconfigure with this upgrade.

1. Do I need to do a fresh install of Catalina? And thus have to re-configure my usb-monitor?

2. Can I mirror the current 250-gb drive onto the 1-tb SSD that replaces the DVD superdrive, and then mirror back that image onto the second 1-tb drive that will replace the 250-gb drive? My usb-monitor and mysql database shouldn't need re-configuration.

3. Will APFS not supporting TimeMachine effect this migration?

4. Or, just what is my best migration option? My current MacOS, app, and data arrangement are just like I want. Now, I just want to replace the disk it is on and add an additional disk. I've got plenty of cloud and extra usb drive storage to work with.

Answer 1

Personally, I've lost all faith in Time Machine in recent times.
I'd approach this as a cloning exercise.

I'd go with Carbon Copy Cloner [just because that's the one I know best] & do as your 2nd suggestion.
Clone to the DVD replacement, test, add the new larger SSD in place of your old HD, clone again. Remove [or just temporarily disconnect] the 1st SSD to test again.

If all is successful, wipe the intermediate SSD. If at any point something goes wrong [which barring human error it shouldn't] - you still have the original HD as belt & braces.

Once finished, neither you, your software, or your sql will know the difference.
One final check once you're done - open System Preferences > Startup Disk & make sure the new boot drive is already selected [it should be, but I've known it miss very rarely]

One thing to note when cloning:
Rename the new drive to something else first, so you will then be cloning MyDrive to MyDrive Clone.
Once the clone is complete & you are sure you can boot to it, change the names again, to MyDrive [from MyDrive Clone] & MyDrive Old [from the original]
This
a) makes sure you don't lose track… or indeed your sanity &
b) keeps anything that was reliant on the drive name sane too.