When you say that you have a medium sized farm tractor, how big is it? Cedars are about the easiest tree there is to take out. Shallow roots and soft wood make the just about pop out without much effort at all compared to the hardwoods or certain types of pines.
For select harvesting, whis means just taking out cedars, I use my backhoe. I cut the roots on either side with a small, shallow trench, then either push it over with the side force of the boom, or change positions and push it over that way. I can do allot of trees in a day. Getting them on the ground is the easy part.
What are you going to do with them? If you are just burning them, then draging them to a burn pile is easy enough. Just wrap the trunk with a chain and pull it over to the burn pile. One of the added bonuses to draging trees is how nice of a job they do smoothing out your land. For roads, I love to drag them over the same route. For pasture and large areas, I go a different route each time.
When I get the cedar to my burn pile, I cut the limbs off and then the trunk into 8ft 6in lengths. These come in handy for all sorts of things. Fence posts, gazebo's, porches and when cut in half, they are awesome shelves!!!
If you hire a dozer, be sure it's big enough to actualy be productive. I know you can get a tree out with a small dozer, but teh amount of time it takes is silly compared to a bigger dozer. My dozer is 168 hp and can push over just about any cedar in one try. Some of the bigger ones might take a few pushes from differen tangles, but it's pretty quick.
The dozer tears up the ground, so I use my backhoe most of the time. One advantage to the dozer is it can push 20 or more trees to the burn pile at one time. If it's all stuff I want to burn, then that's the way to go.
A medium trackhoe would take them out better then a backho, but don't do so well at moving them to the burn pile if it's any distance away. Something over 100 hp should be able to do it pretty easily. More HP would mean faster removal and better productivity.
Eddie