There are a couple ways to do the system image. You can do it after the windows install and updates are done, or you can do it after you install all your software. The latter way is the way I do it. Then if I have to reinstall windows, all I have to do is restore the drive to that point, then update windows and all my software after that point. Much less to do.
After that, then I restore my personal files. Then all I backup after that point is my personal files.
So in the end I have two backup discs. One with all my personal info, and one (actually more than one) with windows and all my software.
About the accounts. Yes windows creates an Administrator account, but it is not one you can normally access. But it also creates a guest account and at least one more account, possible more. So with the two you have created, you have at least 5 accounts on your computer. Don't worry about them. And other than the guest account, I would just leave them alone. And the Guest account is turned off by default.