I think your booth looks great already! I don't think you need to worry too much about one thing overpowering the other - especially since they are all of sock monkeys!
A friend of mine made little "ugly dolls" and she displayed them in a vintage suitcase - we would set it out on a little table where you have your card stand, and TONS of people would stop to see them! Plus the suitcase doubles as an easy way to carry them from your car to the booth space :) I would also think it would be fun, since you do have a few different kinds of monkeys in different themes, what if you did the mommy/baby ones in something baby related (baby bathtub? vintage high chair?) too?
I also think because your products are all related, you could definitely alternate on your tables with one side having the cards up front and monkeys behind, and the other side having the monkeys up front, cards further back.
Hope that helps!
jesi