Heh, it's pretty necessary when doing a dorm in the main 'hood. First bill my students got was $1250+.
Use "moveobjects on" to delete the mailbox on dorm lots. Dorm lots aren't supposed to get bills, but you have to remove the mailbox manually after changing your lot type to a dorm on a user-created lot. Maxis dorm lots already come sans mailbox.
I've found that the "jump rope" option in Apartment Life generates those wacky invisible tiles. I had started up a TALE OF EPIC LOVE between two families in my apartment complex, and their teens were embarking upon their first date, while took place on their home lot because, well, they're poor teens, not the Rockefellers. Unfortunately, Jacob's attempts to impress Tess with his cooking skills went awry because his little sister had skipped rope earlier that day, apparently leaving an invisible tile right in front of the stove.
I'm basing this conclusion on the fact that his sister Katie is the only family member who has skipped rope, and whenever Jacob was directed to cook, he threw the "I can't do that" Sim hissyfit, with an accompanying "jumping rope" icon thought balloon. I've tried the Lot Debugger option for refrigerator invisible tiles, but it didn't seem to do anything.