The Serial Number is located in several places. I will list these in order of simplicity:
- Click the in the upper left of the display and then click About this Mac and you will find your serial number. It is in the last line of the Overview tab.
- Look on the bottom of the stand, the serial number is there.
- Look at the original box the Mac shipped in.
To make migrating from your Time Machine backup External Hard Disk easier the internal storage on the new Mac should be the same size or larger than the old Mac. If your new machine has a smaller capacity than the old machine, return it and buy one with the same or larger storage amount. Then execute the following: Setup Assistant and Migration Assistant. Finally, you do not migrate everything that is on your Time Machine backup External Hard Disk, you only migrate the last backup.