I think most of us here would agree with a clean install of Windows 10. You can easily make a Windows 10 installation USB flash drive using the Media Creation Tool:
Download Windows 10

When you get to the first screen asking for language and keyboard options, press Shift + F10. That will open a command prompt. Then you will want to erase your hard drive by running:

select disk 0

When you get to the option to do a custom install, that is what you want to pick. Then on the next screen highlight the unallocated space on the drive and click Next to let Windows install setup the disk the way it wants to. A few hints to getting a good, clean, successful install of Windows 10:

Have nothing connected to the computer other than the minimum to install Windows; mouse, keyboard, monitor and the installation USB flash drive. If you have blue and black USB ports, everything should be plugged into black USB 2.0 ports.

Do not connect to the internet when Windows 10 wants to connect. That also means if you are using a wired network connection, pull the plug, along with everything else you don't need according to the first hint. Do not connect to WiFi when asked.

When you get to the screen asking for an email to use for a user account - keep clicking the button to skip the screens, or do this later, or I don't have an email address. Whatever button will skip it. You will eventually get a screen that asks for a User Name and Password that you cannot skip. Enter your desired user name there, but do not use an email address! I use John, because that is my first name.

Once Windows 10 finishes installing and you get to a desktop and everything has settled down, then you can connect to the internet and Windows 10 will activate and pull updates. Then you can add any other hardware you need, like the external disk drive. Also, if you want to use a Microsoft account login, you can change the local user account to use a Microsoft Account login.

We also recommend making a second local user account, changing that to an administrator, don't forget the password, and not using that account regularly but just leave it on there available for emergency use should something happen to lock you out of or corrupt your user account that you regularly use.