Are there any plan to add user groups and/or groups into XMB 2.x?
I might start looking into PHP tutorials to help with the system in case I learn anything.

We added a few, but did it by altering our members table (very carefully, mind you) with an extra column called "status2." In this case, we have a development forum and I wanted to give our member developers access while giving them a nifty little badge by their username in posts and their profile.

The key to this was 1) allowing NULLs and/or 2) setting a default value.

As always, do tons of backups. And when you think you've backed up enough, backup again.

If you're running a local instance of mysql you can use this:

mysqldump -u usernamehere -p DBNAME > backup.sql

This is useful because it will allow an exact reconstruction of your database at the time of the backup.

We backup the full site at least daily or during any major code change.

The database is backed up every 8 hours.