Install Win10 on your device.
Install Win10 on your device.
Currently, there’s no clear way to obtain an ISO of Windows 10 simply by entering your product key. The FAQ recommends upgrading first. For a fresh installation at some point, you’ll likely need a blank USB drive or DVD to extract the ISO. You may want to use specific tools like the one from Microsoft: http://wudt.codeplex.com/. Upgrading offers a small advantage if you have Media Center installed; it provides a DVD playback feature that disappears once the service ends. It’s uncertain whether this app will still be available after a clean install, but it may remain linked to your Microsoft account, allowing you to reinstall via the App Store without re-downloading.
You could be mistaken, but once you switch to Windows 10, the system should include a 'reset' feature that lets you perform a fresh installation without needing to download ISO images or other files.
You'll need to reinstall everything, yes. It could reset your SSHD together with the SSD. You'd have to restore the data afterward.