Hey! Saw your post on Discord and came to check out.
Could the money income be tied to benefactors? Those only extist as a numerical value, I would expect to see the money under donations. Little is known about how benefactors work, like long they "exist" before expiring and the rate they give money. The probablity of a happy guest leaving the zoo resulting in a benefactor is currently unknown, as for how much a guest needs to be happy to count as potential one.
The restaurant capacity can be changed, I believe I've seen buiding capacity lines somewhere when messing with original game files. Most game "coding" are easy to look into with a mere notepad or Visual Studio Code. The exception seems to be dll files (for me) and the compiled stuff.