What do you think is the best approach to modeling an entire game world? Would you split it up into chunks? If so, how big would these be in, say, sq. feet or sq. meters?

The answer is 42.

Seriously, though, there is not just one right answer to this. The answer is very subjective, based on what you are trying to accomplish. Splitting up the world into chunks is, of course, a good way to go; but the size of the chunks will be something you need to tune for yourself in order to get a good balance between ease of asset creation, speed of loading, and impact on rendering performance.

Oh. I see. I think I need a balance between the speed while creating those assets and also the other factors like rendering, collision detection, loading, etc.