Sounds like a good plan. I did something similar with my previous setup. I know for sure you can resize partitions with Disk Utility, did it several times with HFS+ formatted drives, but I hadn't had the chance to do it with APFS. APFS drives should work just fine though, or even better since APFS supports containers which are supposed to be easier and safer to work with. Obviously, do that after you've successfully migrated all your data to the new drive, or make sure you have a full backup, you don't want to take your chances with that. Let us know how your new drive works!