Well, thats a tough call because so many user made animals crash the game.
I suppose if there are animals that you have used a lot and have never caused crashing issues that you really really want to use you can go ahead and add them, just be sure to also add their UCIs to the folder and list them in the word document under your name.
Remember to limit your adds to 10 download UCIs (one pack, like a rock pack, is one download UCI) due to the games UCI limit.
It may be prudent to use only single animal UCIs rather than animal packs though, as individual animals within a pack may cause crashing issues.
As to number of animals you can add, I did 7 for the show complex and entrance, which made it a complete square because I was working the area rather than the number of animals, so maybe we can say 5 new animals per turn?
That should leave enough room for other people to build too, and you can always take another turn, I imagine Cricket will take another turn when she has time too :)