if you get one could you fill it with an adopted pet?-curious:P

As long as the pet slot is open, you should be able to adopt a pet, yes. Mostly when you get an extra pet slot (apart from the 5 standard one), you'll need a gold account to claim it :)

Yes, you can fill it however you would like. You just need to have a gold account in order to adopt more than 5 pets.