Guide on adding a new model, animation, and creature to HoMMV

I don't think the performance issue is relevant for this game at the moment, as it can already be played on any old computer, and even increasing the polygon count of the models is unlikely to have any impact.

Well, that's what I think. I enjoy running the game on my old laptop, and theoretically, I'd like to be able to run it on my Android phone as well. Plus, we don't know how the game will react if it's heavily overloaded. Therefore, I think it's best to keep the models around a decent 10k polygons (considering that in the original game, they range from approximately 2 to 7k). 10k is also a standard for modern mobile games. In principle, the models from Heroes 7 are already around that polygon count, so they don't require additional retopology. (although it makes sense to use LODs for the global map; in Heroes 7, most models have them and can be generated with just two clicks).
But here's the question: if a two-sided modifier multiplies the polygons, instead of a harmless 10-12k, we get 20-25k, which, I agree, is not ideal considering that the game engine was originally designed for models with 3k polygons.
But even here, the problem can be solved simply. You can simply separate the elements of the model that need to be two-sided into a separate mesh and apply the two-sided material modifier only to this mesh in the game.

Added 1 minute ago

Understood, accepted. We'll keep working on it.)

Great, this will help. We'll be waiting.)

Well, in general, you could say that. Cheap and cheerful, but it works.) The main thing is to make sure that the bone hierarchy is preserved when converting formats.

This can also be described. It should be clear to a beginner.