If you do go down the Daz3D route... then the right assets are going to be critical.
They exists, but the problem is that, unlike for a "future setting", you can rarely mix different period of times.
While you can take something like a dystopian cyberpunk bedroom, and make it be the interior of a 70's utopian lunar base by example, without it feeling odd, you can difficultly do the same with a viking village and a medieval interior, or the opposite.
Therefore, it firstly need that he dedicate a long time browsing the different shops. And, while it's obviously not legal, also browse the piracy sites, where he'll be able to find some interesting assets that aren't sold anymore.
Then, once done he'll have to pass some times adjusting them, because some are for 3delights, other for IRay, and they'll be either for Genesis 3 or Genesis 8 (some even being for Genesis). There's tools to help him doing this, but it's obviously not 100% direct.
From my point of view, it also need to learn at least the basis of assets tweaking. Just knowing how to change a texture can permit, by example, to use the same room for many different places, without it feeling wrong. They'll have the same geometry, but don't effectively look alike thanks to the different textures.
I don't say that to discourage him, it's totally possible. But it will need more preparation time than a game in a modern or futuristic setting.