Sros,
Agree with all above comments... and ofcourse as noted, with no pictures or description of the site, any advice needs to be adjusted to terrain. Will add below:
1. How much topsoil should be removed?
Really none, unless you need to use it somewhere else, because you will need to replace whatever you remove...alot of extra work... you want the road to be at a higher elevation than surrounding ground to assist drainage. If you remove a strip of topsoil, say the length and width of the driveway, you basically just created a trench... Trench's hold water. In theory, the ground you are going to build on, unless it is plowed farm ground is compacted... leave it that way and build from there. Contour the ditches and make the crown using the compacted earth as the top of the drive way. Never under estimate the power of gravity and use it to your advantage... Water always seeks the lowest point and the path of least resistance.....
2. Do I need a weed blocker? What kind?
No, because on a gravel or rock driveway, there is none, except after the fact, liquid herbicides (weed killers or Roundup). The weeds grow on the top, not from down below the road. But if you are willing to spend the extra money, probably significant dollars depending on the length of driveway, you could put down ground fabric over the base material, under the top coats. This does not prevent weed's however, it keeps dirt and mud from seeping into the top layers of the road material.
Weeds grow, even in rock roads because the seeds lay on the top, and work themselves into the rock crevices and sprout on the top layer of either dirt that has blown in or dust. They require very little material to grow. No su-layer will stop this, the only way is to either use chemicals or scrap the road and by basically pulling them out. It never ceases to amaze me how weeds can withstand the heat, and little water yet flourish. The person that can get a weed to look like just like grass will became very rich....
3. What size stone should be used as a base?
As large as possible and economically feasible. Also, dependent upon your use. Just cars, not trucks? Preferably at least 2-3 inch hard rock base. Avoid if possible limestone. While it is the cheapest material, it basically degrades and breaks down over time. You want to find some type of angular stone, rather than round, especially for the top coats as this will cause the material to "lock" in place and become stable. I have a couple of neighbors that went with pea gravel. Looks nice, but is always moving around and when it rains, it becomes like ice as the stone slides past each other......
4. What size stone should be used on top of the base?
Working from above, going to 1 inch, and then down to 1/2 - 3/4 inch.... you can always top of with fines, but realize when you plow, these will generally come off.....also, they can create some muck, especially if you use limestone....
5. When calculating how much stone you need, how do you convert cubic yards into tons? As noted by others. See previous post....
6. Do you build the crown before you lay down the stone or after?
As noted by others, always build the structure first, then lay the stone down.
7. What is the best tractor implement to maintain a driveway?
Probably the most common is a box blade... rear straight blade also works, but not as exacting... Another feature that would assist is a 3-point "top & tilt" device on the boxblade to maintain the contour.... An FEL pointed down in reverse mode could also work but again is fairly inefficient compared to above....
Sound like a fun project...... /forums/images/graemlins/smile.gif