You don't need the college codes. You can look them up through the CAT.
All the profile info is optional. In fact, many schools claim to ignore it until you apply.
As far as when you can get to the test center, I'm pretty sure you can't hang out in the test center itself but you may be able to wait in the lobby or hallway of the building where the center is located to gather your thoughts or what not. That would probably depend on the specific site to which you're travelling, I would guess. Can you call ahead to confirm?
Hope that helps and hope you rock the GMAT.
Thanks alot !!!!!
Thanks for your wishes !!!
Kudos to you !!!