Solved How to backup and clean install? Specific situation

Hey, guys, so I need your help.
I have an ASUS laptop with pre-installed Windows 8 Home(UEFI). I've additionaly installed Ubuntu alongside. After a while, I wanted to uninstall the Ubuntu and install another distribution but I wasn't sure how to do that, and the guides online just made it worse, as I formatted the Linux partitions but couldn't uninstall GRUB. So, now my HDD looks like in the attachment.
I have the possibility to upgrade through Dreamspark to Windows 8.1 or to Windows 10, but would like to have a clean install.
So, my questions are:
1. Should I get Windows 10 EDU or Windows 8.1 Pro? I'm not sure W10 is ready, and having the 8.1 will give me the possibility to upgrade later.
2. What do I need to backup and how do I do it? I don't really have an external HDD, so I can't backup all my data on the D:\ partition. How do I backup my current W activation key? Will I need the restore partition? What about the recovery? Ideally, I would like to have a clean install, formatting everything, except D:\.
3. What is the correct way of uninstalling Linux?
What do you think? And sorry about the mess on the HDD.

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