Did my Time Machine backup copy over properly?
Time Machine does not make a 100% perfect copy, nor does it necessarily make a BOOTABLE copy should you need to swap it in suddenly one day.  A better way to upgrade to a new SSD (don't spend all that time only to put in another slow spinning drive that only lasts 2-3 years these days!), is to also purchase a usb-to-sata transfer cable for $10-$20, use Carbon Copy Cloner (CCC) on the old mac to make a bootable mirror image, including the hidden recovery partition (and possibly update it!), then swap drives and go about your life.  Optionally wipe the old drive to use for testing or backups if it's still safe to use at all.. likely not if it's several years old.  CCC is a fantastic paid backup app, but I think you can get away with making a full bootable clone without buying it first.  This may have changed.