Clean Install Windows 10  

A few questions...
I already did the upgrade on the original hard drive which activated OK. Can I swap the old drive for a new larger drive and do a clean install, will it still activate OK?
I made a USB recovery drive after upgrading to Win10, I also have a bootable Windows 10 installation USB as described here. Does it matter which one should I use?
Any thoughts on preparing the new hard drive for a dual boot system? I was going to install Windows 10 first, then Linux.

Q1 - As long as your Key is with you or in your BIOS (If your PC came with Windows 8+, it will automatically store the Key in BIOS so no need to worry).
Recovery Drive is for repairing your PC if files or anything else is damaged. Installation media is designed for Clean Installing.
Linux, what distribution, Ubuntu will automatically install GRUB boot loader, make sure you select the right partitions to install Ubuntu on.
When Ubuntu is installed, make sure that it is the first in the boot order otherwise you will miss the GRUB boot loader and boot into something else.
Reply if you need help.

The PC is a Lenovo ThinkCentre M53 Tiny, which only has room for one drive. The specs say "Windows 7 Professional 64-bit Installed; Comes with Windows 8 Professional 64-bit license". There is no sticker or printed material with the keys, but I ran nirsoft's ProduKey and found different keys for Win 7 pro and another one for Bios OEM key. Will those work? Or should I clone the drive?

The Windows 8 BIOS Key will work for Windows 8, Windows 8.1 and Windows 10. For the Windows 7 Key, if your PC came with Windows 7, the Product Key should be on the box, if not, you will need to jot it down somewhere safe so that you can remember it.

OK, thanks. If I did a Windows system image backup before swapping drives will I be able to use that on the new drive after installing the dual boot, or should I just start a new backup? I don't want to mess up anything.

Might be a good idea to make a New image backup of your c-drive so you know you have a current backup image. Also you could use a app like Macrium Reflect for making your backup, and also make a Rescue disk, using Macrium Reflect. its a Free app. :)

After installing Macrium Reflect and making your rescue disk (USB stick) You can also restore that image to your new drive too.
Just always keep your image backups on a separate drive.

Rescue disk ehhh... I recommend Avast's Rescue Disk 2016, it is completely free! This is for use in ase
your PC has been infected, it will scan all partitions and sectors including hidden and revemapped. For the back up, Macrium Reflect is good as Mike explained.

MSMPlayz said:

Rescue disk ehhh... I recommend Avast's Rescue Disk 2016, it is completely free! This is for use in ase
your PC has been infected, it will scan all partitions and sectors including hidden and revemapped. For the back up, Macrium Reflect is good as Mike explained.

Just so you know, Making a Macrium Reflect rescue media disk (usb or dvd) has nothing to do with any kind of virus protection. Its for only restoring your computer, incase user can't boot to their OS for whatever reason. Can also repair corrupt boot system files too. Making this, is the best insurance to get back the users OS incase of changes made, mess up the users OS.

Ok, however, if your OS fails to load, you can go in to advanced options and Reset your PC there. Better idea, easier and (Probably more safer and efficient).