Also, what you're experiencing is not limited to Windows 10. If you change an account name under Windows 7 for an existing account the folder structure is not replaced, but will maintain the naming convention formed when the account was originally created.
Under Windows 10 all account management is under Settings -> Accounts. Not knowing whether you wish to create a Microsoft account linked Win10 user account versus a strictly local Win10 user account I cannot advise further. There are myriad tutorials out there showing, step-by-step, how to do either including screen shots. All you need to do is a web search on either "create Windows 10 Microsoft user account" or "create Windows 10 local user account" and you've got what you're asking for.
By the way, you're very smart to stick with Windows 10 if your intention is to stay in the Windows ecosystem. You said it perfectly in that soon enough there will be nothing but Windows 10 and it's insane to use any unsupported OS if one intends to interact with the internet, and who doesn't on the vast majority of PCs out there?
Edited by britechguy, 30 January 2018 - 02:59 PM.
Brian AKA Bri the Tech Guy (website in my user profile) - Windows 10 Home, 64-Bit, Version 1803, Build 17134
. . . the presumption of innocence, while essential in the legal realm, does not mean the elimination of common sense outside it. The willing suspension of disbelief has its limits, or should.
~ Ruth Marcus, November 10, 2017, in Washington Post article, Bannon is right: It’s no coincidence The Post broke the Moore story