How big is immense? The Steam page is pretty light on specifics about changes from the original Spintires game. I'm a huge fan of Spintires so am looking forward to seeing how this title turns out.

Depends the sight....
For an ant, 1km x 1km is really immense lol

With mod you can up to 1x2km (for now) so y think you can up to 2x2 km without probleme
1x1km it's too small