The thought that went thru my mind is that trying to combine wheat and get that straw baled right away - before it gets wet - may push you.  That is where I think it would pay to have the wheat custom- combined, and then you can concentrate on hauling it away, and getting the straw baled. 

Spreading fertilizer (yourself) and running a drill (yourself) would not - should not - conflict with harvesting.

Just my way of looking at it.