The site allows you to customize colors and wheel choices for now, but more features/selections should be added in the near future.
The "interior" section is incomplete (see below).
Model 3 Interior Is Still A Work In Progress
Additionally, a video of the configurator popper up over the weekend. The video captures the Model 3 choices from the "design studio."
"In the future there will be more photos/angles that you can play with. There's no interior section yet, but will be added soon"
"This site was encouraged by fans and created by an eager Model 3 reservation holder. It is intended to be fun. This site is in no way affiliated with Tesla Motors. All photos depict fan made mockups of prototype vehicles."