I think I would invest some money in hiring a motor grader to put in uphill side ditches and grade the road with proper crown. A good operator with a large motor grader could do 1/4 mile of road in a day easily. Then with the road bed properly shaped, the dump truck driver can spread the gravely pretty well by just chaining the tail gate to only open a small amount and then driving forward as the bed is raised. It may require a little bit of levelling afterwards but not much.
I would go with 3" stones for a base then after compacting it, top it with 3/4 crusher run rather than solid crusher run. You need the large stone base to keep it from sinking into the ground.
Also IF and that is a big IF, you can determine culvert location prior to putting in the gravel, it will be much better. Why disturb your road base if you don't need to by digging a wide hole across it for a culvert.
As for equipment, a land plane is going to be far improved over a straight blade for shaping and maintaining your road. If you use a hired motor grader to put in your ditches and crown the road bed, you wont even need a straight blade for anything. I don't know if you have ever used a blade, but they are very easy to get dips and dives in the road surface and the more you try to remove the high and low spots the worse they get due to the tractor following the contours and the blade just cutting more and more each time the tractors wheels ride over the hump or dip.
