1 - Even though it is described , I did not need the ia32-libs with my versionIt is actually described in "Install Oracle 11gR2 Ubuntu Linux 11.04 (64-bit)"
2 - Which is the best method for setting environment variables (ORACLE_HOME etc.) permanently for all users?I would rather not add ORACLE_HOME for EVERY user. You could check for the users group, e.g. dba, or create a new group like "ora11g" for non SYS access, and then add something like the following to /etc/profile, which is read at user login.
for group in `groups $USER`; do if [ "$group" = "ora11g" ]; then export ORACLE_HOME=path_to_oracle_home fi done
3 - I used a startup script described here: http://www.oracle-base.com/articles/linux/AutomatingDatabaseStartupAndShutdownOnLinux.php to start Oracle instance.You need to add "emctl start dbconsole" to the script start EM dbconsole.
4 - Before reboot, all works fine. After reboot, the Oracle database instance is working (I checked some queries with SQLPLUS), but not the Enterprise Manager