It's easy to add more folders to Outlook - right click on any folder and choose New Folder. You can change the folder type, if necessary, and change where the folder will be placed. You can put folders in the "root", along with the Inbox, Calendar, Contacts etc, or as a subfolder of any folder of any type.
To delete folders you no longer need, you could right click and choose Delete Folder or select the folder and press Delete. Both of methods result in an annoying delete confirmation dialog. It's especially if you have several folders to delete. You can eliminate this dialog if you just drag the folders to the Deleted items folder.
In older versions of Outlook, reminders only fire from the default folders.
Events in other calendar folders are not listed on Outlook 2007/2010's To-Do Bar.