You'll need some kind of scale to determine pre-load. A torque wrench will just get the nut tight, but not be able to tell you how much force it takes to rotate the hub. I was a little confused about that part too, but now that I've done it a couple of times it makes sense. You use the spring scale to pull the rotor around to make sure that the hub nut is tight, but not too tight. Too loose and things could move around killing the bearings (or some other catastrophic failure), and too tight will kill your gas mileage.
Also, you don't need a bearing press. The bearings just drop in and are held in place once everything is tightened down. To get the bearing seal in at the back of the rotor I just used a 2x4 laid flat across the seal and then gave it a good whack with a rubber mallet. Seats the seal in nicely.
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