I can finally contribute meaningfully to this thread!
Last winter I invested in a Husquavarna Rancher 460, new. I'm sure I could have spent less, but fixing tools and knowing when they are a good deal is not my specialty, so I went for the warranty. The maximum bar for the model is 24 inches, which came with the one I bought. I got the Granburg Alaskan chainsaw mill, and an OREGON 72RD084G 84 Drive Link 3/8-Inch Ripping Saw Chain Standard Sequence.
This combo has worked fantastically for me. I felled a gum tree, cut it into 10 foot sections, and started ripping. once you put the mill on the chainsaw bar, you get a maximum of 17 inch width or so, which was less than the bottom trunk width. So, I got some friends over, we cut until the log was too wide, then gave it a quarter turn and cut from that side, which was enough to get through it for all but the lowest section, which I gave up on. Other than taking one side off, I left everything as live edge wood for now. Gum wood is famous for warping like mad while it is drying, so for the most part I went with 3-inch thick planks. I would have made them thicker to be safe, but wet wood is heavy, and I don't have any machinery to help with the lifting. I cut one board a bit over 4 inches, and two of us couldn't budge it until I'd cut it into 2 5-foot long sections. I decided I'd take my chances with the warping to have longer boards.
To start: you can buy or make metal rails for the first cut, but I'm a wood person. So, I took 2 short 2X4s, and screwed them to each end of the log, then stood two 2X4X12 on edge and screwed those to the short pieces. I then set the mill to cut just below the short pieces. My first cut could have been thinner, but it was even, at least.
As far as keeping the boards even: it didn't go too badly - once the chainsaw is into the wood, the mill really does balance reasonably well, and it isn't like you have to fight the weight of the saw to keep it on the surface.
Strain on the chainsaw engine: its too soon to tell how well the saw will hold up. However, it did take a bit to figure out how to keep from overwhelming the saw and stopping the chain. The key was 1) don't push the saw forward to hard. Just be patient and go slow. 2) rock the saw a bit. Cut an angle on the near end, then pivot and do the same on the far end. That way, you aren't cutting the full width at once, and it is harder to stall out the blade. Also - be careful when cutting logs close to the maximum - a little bump and the saw won't move, and it might take a few minutes to figure out why. along the same line, sometimes the end would be a bit uneven, leaving a lip on the log. On the next cut, the mill would get caught there, and I'd be left wondering why my saw wouldn't cut the last inch!
Posture: If you have large logs on the ground, experiment with the warrior 1 yoga pose. Or squat, or kneel. Don't just bend over, you will kill your back. If you are lucky enough to be situated on a hill, fantastic. If you have the manpower and your log is light enough, you might be able to roll and maneuver it so that one end is propped up a bit. If you can, it is worth the trouble. Obviously, if you have heavy machinery around, you can lift it onto some sort of braces, and run the mill at standing height. I didn't have that, and it still worked.
Gas consumption: one cut took somewhere over 1/2 tank of gas. So that is about 14 square feet of cutting. I've been meaning to count my boards, at which point I can give a more accurate estimate of how much gas I burned to do this. I'll try to do that tomorrow.