Non-venomous snakes like boa are OK too. It just needs existence of heated room that visitors can go into.
Macaws are rather loud and often pluck their feathers - but are popular, if you can "rescue" some no longer wanted tame pets, I would add it.
Flamingos depend on solid source of water, if you have stream or your own water-well, you can afford them. Their dayly upkeep is not more costly than similar sized waterfowl. Also initial investment would be higher, so up to your budget.
Leopards are very dangerous despite their smaller size (while pumas seem calmer on average). If you can´t give them too much area, you should compensate it by hight and many inner climbing structures. Their enclosure must be very solid, with full metal net over it. Leopards paws can never reach visitors, so either glass wall or fine mesh or double bars (don´t believe visitors will behave reasonably, alsways expect the worse). At least 2 boxes/cages per animal so you can clean them. Padlocks on all doors. Liabilty insurance. Pray that they don´t become seriously ill otherwise you will pay small fortune to vets able/willing to handle them. And visit at least 2 zoos before you build anything, and copy their system of doors and safety protocol for large cats. Escaped serval will be headache, but escaped leopard might cost you zoo licence or land you in jail.