As to bar and mill size. Get the 48" mill. As a general rule of thumb, you need a bar that is 6" longer than the log you are milling. This six inches is eaten up under the clutch cover and at the tip. You want to mill 32.5 inch logs. Not saying you absolutely can't to it with a 36" bar but this eliminates use of the chainbreak and gets you to close to your sprocket. Also, that 32.5" tree at the base may have swells, or you may want to cut through limb extrusions or crotches that make it much wider. Why risk it? Get the 42" bar that you know will work and not worry about it. With that said, you should also get a 36". Having too much bar raises other issues like bar bowing and encouraging you to seesaw your cut. The smaller the bar/chain the greater the power though that 3120 will give you sufficient power for a 42" chain. If you are serious about milling, you will end up with many bars. When you nail out part of a chain, you can cut it down to a lower size. Have fun but remember: " the spice must flow" oops. I mean " the OIL must flow." Skip chain? Well, it is much less cutters to sharpen and throws prettier ribbons and. Less dust too.