Can I use Acronis to go from a larger drive to a smaller drive?

In simple terms yes True Image can lay down a backup image from a larger drive to a smaller capacity drive as long as two conditions are meet.

1. The total data on the source disk is less than the total capacity of the target disk being restored to.
2. You do not use sector by sector method for the recovery.

As for your GPT MBR question the way to avoid any problem is to fully prepare the new disk prior to attempting a recovery to it.  This is an easy process using Disk Management in Windows.

1. Attach the new disk to the PC
2. Open Disk Management and a popup screen will appear asking how to initialize the disk giving you the options of GPT or MBR.  Generally an SSD will have GPT selected by default.  Click on OK when happy with your selection.
3. Once initialized, hover your mouse over the graphical disk representation and right click on it.  Select Create Simple Volume which will start a Wizard which will allow you to configure the disk for formatting. Once that is done the disk is ready for use and can then be used as a recovery target disk.
4. When you boot the PC for the recovery of the backup image to the disk insure that you boot the media used in the correct boot mode, UEFI for GPT - Non UEFI for MBR.  You will see two choices associated with the boot media when you attempt to boot to it.  One of those choices will have UEFI in its name.  Select this one to boot in UEFI mode.  This will prevent any change to your fully prepared disk.

Ok, thanks.

I was thinking of buying a USB drive to use as sort of a intermediary weigh station. i.e. take the files from the 1 TB SSD (now 4.5 years old,) transfer what I can to the USB, and from there, transfer the files to the new drive. Lather, Rinse, and Repeat, until I have cleaned the 1 TB (current) drive as far back as I can.

Unless you have another idea...

Worst case scenario: no significant space reductions made. Well, in that case, I'd have 173 GB left of Free Space on the yet to be purchased 500 GB SSD (all that *should* be on the drive is Flight Simulation related stuff.) At least that is the plan. The other Files I'd put on my Linux system, which is on a 1 TB NVMe drive...

Thanks in advance.

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