I don't see any such link in the CS, or under the CS tab. I know I can buy pet slots from the Pets page however. As a pet slot is normally 2000, does this mean it is 1000 as of the black friday sale?

that is correct, and this is the last time Pet Slots will be half off.

Yes, I know...however, what about custom pet overlays, where would I go to buy that?

also on the pets page. There's a "Custom Overlays" button on the top between "Job Agency" and "Name Exchange"

Thanks!

Yep, pet slots are 1000 CSC each (just bought three, lol).

As for upgrades, it depends on what you are looking for. Gold Account Medals are in the CS, but other things are elsewhere. Username Change is found on the User Dashboard link (under the personal tab), just look for the link that says "Change Username". Pet Slots are sold on the pets page. Name Exchange is on the pet pages. Changing a pets name is in each individual pets drop down menu.

No problem!

Thanks.