Can you have birthday parties there? Is it a spot or venue inside the zoo we can rent to have one if so how much is the cost?

Yes you must contact them

Yes, but you have to contact them about pricing and availability.

Yes

They allow events. You would have to Contact them to see prices. (Event price vs admission)

Yes, there is a pavilion for parties inside the zoo. I'm not sure about the cost, its listed on the website.

I know they have a pavilion area available for rent for special occasions, they also have several different "behind the scenes" type packages for a more involved zoo experience. I strongly recommend calling to find out about pricing and availability or visiting their website to see some of the features they offer.

Zoo official will be the best to answer. I have seen a place by train station inside for parties.