We could look at the file sizes of the original stages and go by that. Or we could start from scratch using Mewtwo2000's Fountain of Dreams stage as the base. That stage has over 170 models in It If I remember correctly.
Don't, do it, it's not a good reference. I mean, I got bigger stages working flawlessly. FoD is just full of animations, and those take memory too. It's not all about filesize, but elements used by the stage too.
The only option is test and fail, and when you fail, trying to decrease what you got.