Stuff like that requires massive (relatively to this field) amount of data to be stored. While this is no problem when you can phisically write stuff on a support such as an e-card, writing all of those bytes via ACE is unfeasible, it's just too much. When you need to write a lot of data onto RAM, the way to go is something like this: https://github.com/E-Sh4rk/EmeraldACE_tuto/blob/main/hex-writer.md
You can see a demonstration of how easy it is to write entire Pokémon (in this example Ageto Celebi and Whismaker Jirachi) from scratch using that method here: https://github.com/E-Sh4rk/EmeraldACE_tuto/blob/main/generating-pkmn.md
By comparison, writing an entire Pokémon from scratch using just ACE codes would require several (about 10) codes and any mistake would cost you the entire process. You can see yourself how this scales to larger projects such as the one you suggested. Depending on how large the amount of needed data is, using an even more advanced ACE evolition such as this might be a better option: https://github.com/E-Sh4rk/EmeraldACE_tuto/blob/main/hex-editor.md
Since the hex editor requires itself quite some time do make, it might or might not be more efficeint than just using the hex writer