1) There should not be any autoupdates by default. The little icon up by the clock controlled by the yum-updatesd service will notify you when packages are available, but should not install anything unless you tell it to. If you want to disable this notification, you can do
# service yum-updatesd stop
# chkconfig yum-updatesd off
You could also go into /etc/yum.repos.d/* and set ENABLED=0 in all the config files, as well as all the repos in /etc/yum.conf. This will prevent you from being able to use yum for anything including installing new packages, so not recommended
2) Rolling back packages can be difficult. RPM and yum will complain if you try to install a version older than your current one. Typically the best way is to remove the currently installed version (yum remove <packagename>) and manually download the version you want and install it. However if other packages depend on the one you are removing, you would have to remove them as well. Then you'd have to go back and download and install the version of each of those packages that corresponds to the version of the package you are rolling back. If you haven't done much configuration of your system, you may want to consider just reinstalling and leaving it at the version you want.
3) You can probably get rid of the floppy mount in the Removable Media preferences. You can set what you want it to automount or skip. Skipping your floppy (probably /dev/fd0) should prevent this from happening.
4) No idea with the screensavers, why not just take it off random and pick the one you want?
Hope this all helps.