read more carrefullty the documentation and the man page, it's very clear and what you want is very basic.
in the man page of Xvnc (it's the true programmewhich is launched by vncserver), you can see that Xvnc can be launched by inetd at the startup like a service. This can perform a server wake up on demand.
In all case, you don't need to be root to launch it. vncviewer connect to the vncserver at the port that the user launched. The GUI you obtain is the GUI that the user use normally or you can configure the xstartup file in the $HOME/.vnc directory to launch the window manager you had installed on the box.
In the case you use the browser, all the user connect at the same port share (if it's enable in vncserver config) the desktop.
if you launch vncserver on many screen, they are available by browser at http://yourserver:58xx.
xx means the screen where vncserver run : 00 for screen :0, 01 for screen :1, and so on.