So, I would like to create a mod that replaces all units and, possibly, heroes in the game. The Factions will remain the same.

I already have ideas for 4 Factions:

Inferno

Beasts -> Furies <-> Megeras (Complete reskin)
Trogolodites -> Hell Trogolodites <-> Chthonians
Hunters -> Stalkers <-> Shadow Hunters
Twilight Witches -> Shadow Mistresses <-> Mistresses of the Night (body, arms, and head of Djinns from Heroes 7)
Manticores -> Scorpicors <-> Ancient Manticores
Minotaur -> Minotaur Guard <-> Minotaur Hunter
Dusk Dragon -> Dark Dragon <-> Red Dragon

Conflux

Kabiri -> Elder Kabiri <-> Fire Imps
Gargoyles -> Obsidian Gargoyles <-> Elemental Gargoyles
Golems -> Arenite Golems <-> Jade Golems
Luminary -> Radiant Luminary <-> Ice Luminary
Djinns -> Djinn Mediums <-> Djinn Viziers (all male)
Rakshasa -> Rakshasa Raja <-> Kshatri Rakshasa
Colossus -> Titans <-> Shanti Titans

Castle

Hunter -> Ranger <-> Sheldon Marksman
Fairy -> Nymph <-> Oceanid
Bladedancer -> Blademaster <-> Sea Dancer (a pirate from Heroes 7, but in a new style)
Druid -> Druid Elder <-> Sea Druid
Unicorn -> Light Unicorns <-> River Unicorns
Ents -> Ancient Ents <-> (not yet invented)
Green Dragon -> Emerald Dragon <-> Pearl Dragon

Haven

Marksman -> Marksman Veteran <-> Archer
Wolf -> Fierce Wolf <-> Battle Wolf
Nuns -> Preachers <-> Vestals
Guardian -> Legionnaire <-> Zealot (will use models from Heroes 7, but instead of a spear, they will have a sword)
Chaplain -> Abbot <-> Healer
Cavalier -> Cerberus <-> Knight of Light
Angels -> Seraphs <-> Celestial Warriors