RTF is a global modification that replaces all towns in the game.

Which version is required?

3.1 (it might also be 3.0, but I haven't tested it on that version.)

And how complete is the mod?

For now, the Elementals and Dark Gnomes are ready. Humans, Lizards, and Nagas will be subject to some changes, while Orcs, Undead, and Magic Chimeras are just an idea, nothing more.

I can help with the storyline.

Based on everything written above, it's clear that the storyline is still far from complete.