A couple things, one, depth gauges aka rakers are easy. You need to lay a straight edge across the top of each set of two cutters and see how far below that the raker between them is. .025" is what you want. A caliper works for to measure, but after a few times doing it, it's easy enough to eyeball. A Carlton File-o-plate is the best for determining where each raker needs to be, but they're out of production.
Rakers are easily taken down with a flat file, but I prefer a dremel with a sanding wheel or stone. Much less hand cramping.
Lastly, if you don't already grease you bar sprocket, you don't need to start now. Oregon says they do fine with just bar oil lubrication, and that greasing through the hole can actually force grit and grime into the bearings. Some people grease, some don't. I never have, and haven't ever had as problem.