When the system boots, depending on the runlevel, (5 for graphical login), everything is started in /etc/rcx* up to the runlevel AND /etc/rc.d is also run. No matter what you login as, everything as configured is run. So the firewall, all services, etc are started as root. Virtually all apps will be executable by regular users, and /usr/bin will be in their default path. For apps such as Opera, they are likley added to the start menu, the regular user can just drag these to the desktop. I don't know how you configure the default look of root to other accounts though.
If you use dialup, you may have to chmod u+s /usr/sbin/kppp to be able to execute as non root because only root can dial up and start pppd. Otherwise, you should be good to go.
For ease of maintenance, you probably want to grab Extras-->System Tools-->File Manager Super User Mode to the desktop. When you select it, it prompts for root's password and you can then navigate/change config files easier.