Can’t comment on the animation/video/image editing side of things, but as for your questions:
Is it possible to make platform-indendant derivation ?
Chapter 9. Cross-compilation of the Nixpkgs manual covers this topic in detail. I think the gist is that the majority of Nix expressions will result in a platform-independent derivation, and the compilers during the build process will get called with architecture-specific flags.
Hydra (the Nix continuous build system) automates this with “the system parameter refers to the system architecture that we want to build for, which can be (for example) 32-bit Linux machines, 64-bit Linux machines, 64-bit Mac OS X and so on.”. You check the end results yourself on the public Hydra instances (that I know of): Nix’s hydra.nixos.org (e.g., see job name here) and flox’s Storehouse (see the naming of the list of jobs again).
Also, do you have any general tips for derivation that output data/images ?
Can only say that this can definitely be done; at least seeing all the stuff people have come up with regarding Nix. (By the way, thank you for linking your code!)
Does Nix cache evaluation at a lower level than flake level and derivation level ?
Someone more knowledgeable has to chime in regarding this…