Clonezilla (disk-to-disk copy to clone disks)
If I use this would I have to buy a new copy of Windows or would it still think the clone is the original install?
Depends. Unless the source and target drives are both the same size, things will probably go wrong, assuming the source drive has an OS on it.
If the source drive doesn't have an OS on it, it's perfectly fine, since there's no boot manager to screw up.
Trying to clone Windows boot drives with Clonezilla was not my finest moment. See, the annoying thing with Windows is that there's this Windows recovery partition, and it's placed pretty much at the end of the drive. I tried cloning a 1TB HDD with Windows on it to a 240GB SSD, moving the recovery partition with GParted so that it would fit in that smaller space.
Did not go well; Windows kept complaining that its essential files were corrupted and stuff. Absolute shitshow. I gave up and decided to just reinstall Windows onto the SSD, because that's far easier than trying to figure out how to stop that error. Maybe someone more competent can do it, but I can't. BTW, you can't do an upgrade-in-place and keep your files if you boot directly off the Windows install disk. You need to be able to boot into Windows first. Learned that the hard way.
That was an MBR install of Windows. I've heard that a GPT install would be more tolerant of this kind of partition screwery, but I fear that you'd still get the same error about the corrupted system files.
Overall, I don't recommend it for cloning Windows installs, but my experience is limited.
Also, you don't even need to buy a copy of Windows 10, if that's what you use. Either you can use the Media Creation Tool to download yourself an ISO file or make a USB thumb drive, or you can
skip that nonsense using this article's method (changing user-agent strings). I'd suggest skipping the tool entirely. Just get yourself an ISO of Windows 10 directly (the 64-bit version is what you probably need), and use Rufus to make yourself a Windows 10 install disk. It's the product key that costs money, not Windows itself.
The current version of Windows forces you to make an online account, however. Skip the process of connecting to WiFi (and disconnect all Ethernet cables from the PC), and when it complains, just skip the process and make a local account.
If you were activated before, it'll recognize that your computer (I think it's tied to motherboard) is already activated when you connect to the Internet for the first time. You can safely skip the product key part. If not, you can also skip the product key, since all it does is that Windows complains sometimes that you're not activated, and you can't do any personalization (wallpapers and stuff).
I can't say for Linux. Maybe it's less sensitive to this kind of screwery. I think you'll have to restore the GRUB boot manager using your distro's install disk, at least.