Are there other ways to gain more pet slots than buying the plushies? I'd really like to be able to have more pets, but I don't have fourty dollars to spend every time I want another space.

If you activate a Gold Account you can have 5 more Pets. After that you have to buy the Plushies if you still want more.

Oh that's right XD I forgot about that. Thanks for your help.

If you use the GA, and activates it you get 5 additional slots. So that gives you 10 slots other than buying the Mystical Donadak Plushie and Mystical Montre Plushie.