Can i combine this?

Can I make half plot world and half farming world on my minecraft server? Or is the plot world made with plots across the entire minecraft world? Or can I just e.g. Make 250 x250 blocks with plots and then the rest with no plots?

In my experience, the plots are generated automatically across the world. Creating an additional farm world makes sense, since you can switch on monsters here, which is not recommended on the plots.

The plots are generated all over the world.

With a little programming experience you can reprogram it.