Nice to see you interested. I have no idea how MM7&8 look. I am afraid that more is expected and required, more time/never it gets finished, unless people is extremely motivated. Now if you all decide to go on a MM6&7&8 mod, I will just stick to an Oblivion map and drink a bottle of vodka to burn my anger, as I can't help you on that.
In my first idea, 7 of them are required. As in the game. Now, if someone is perfectionist and goes for having to choose female/male, then would be 14, but do we have 14 creatures with no penalties on melee/shooting in HoMM? I don't think so. Also there is a frame problem, as we already experienced in 300. Can you find 14 defs with a enough high rate frame to be able to replace the commanders? You are the master here.
Weapons are only a graphic matter, it does not affect the damage or the speed.
Creating a new system of skills, as dexterity/stamina is possible only by changing the text. How can someone implement a new combat skill as dexterity in HoMM3? The bow/sword is always hitting and the luck concept is affecting in HoMM very different than in MM6. It would be great, but I have no idea how could be done.
Edit: now that I see, every commander had two ID's. So there are 16 shooting/melee creatures possible. But working on 7 additional graphics just to have a choice from male to female with exactly the same stats...