I can't believe I didn't ask this before but:

I currently don't have a Gold Account and I just bought another Pet Slot with CSC, so I'm currently at 10/6 slots. Can I adopt another pet like this or do I have to buy a Gold Account?

I think you have to use a gold account no matter what when it comes to getting more pets.

Yeah, you can pretty much keep buying slots, but you can't actually fill them until you have a gold account.