Here are some tips on how to keep the guests happy: use restaurants instead of food courts. Place your exhibits close together so the guests don't have to walk as far to see different animals. Use flowers and other landscaping materials, and hire a few tour guides.
Animals: Aside from the White Bengal Tiger, Black Leopard, and Okapi, I would use regular bengal tigers, African lions, giraffes, and other animals that are fairly low maintainence but keep the guests happy. Give the animals plenty of space, but try to keep the exhibits all fairly close together. Happy animals=happy guests!
And just focus on filling up the front part of the zoo instead of trying to fill the whole zoo. Hope this helps! And don't forget to do your research!