Two nit-picky notes:
Be careful with the phrase "single-user mode"--I know you mean that only one person ever uses the machine; it auto-logs-them-in; they never think of "logging out", only shutting down; and so on. But in technical terms, "single-user mode" on OS X means holding down apple-s at startup, which boots you straight to a root shell (no password) instead of the gui. It's intended to save a broken machine by giving you full command-line access. Also, you may confuse people because there is no "setting" for single-user mode vs multi-user mode--it's just the existence of other gui accounts or not. So maybe say something about being the "sole user of the machine", or it being a "shared machine with multiple accounts".
DocumentRoot is already "enabled" (set to /Library/WebServer/Documents). You'd want to *change* its value, which is a perfectly good idea. But then you have some confusion about what .conf file controls what--you can edit /etc/httpd/users/username.conf and ignore the main directives in httpd.conf, or you could change the main <Directory> block in httpd.conf and comment out your username.conf file (so it won't override your earlier settings).
Sorry to be pushy, but I spend a good bit of time in forums answering similar questions and there is no point in confusing people unnecessarily with published material...