First off, you would not "owe" any money at all. They give you some free furniture for your personal space (if you decide to use one). No one is forcing you to go into the mall and purchase the virtual items. As for the hard drive space issue, you should have expected that- 4 GB isn't that big of a deal considering the drive sizes out there now.
If you aren't liking it then I offer a suggestion- highlight it, hit triangle and select "delete".