2) I do like using carbide-tipped tools for the occasional turning that I do, but unless they get a nick, I don't really know when I should rotate the tip for a new edge.
Dan, I use carbide scraping (and Hunter style) tools quite a bit, and I confess that, after several years, I don't have the answer either. I can share my experience, for what that may be worth. First when it comes to carbide scraping tools I make heavy use of all three sides, not just the front end or tip. While the tip may see more use, I will work from 8 o'clock, around the tip, all the way to 4 o'clock. So when I do finally decide to rotate, I don't turn the cutter a little bit, but a quarter turn. To that end the first thing I do with a new tool/insert is to mark the "north" position. With the insert off the tool, I mark it with a Sharpie. I start from inside the screw hole, go across the top, down the bevel and across to the bottom. That way if and when the markings on the exposed surfaces wear off I still retain the marking on the protected surfaces. When it comes time to rotate the cutter I use the sequence north, south, east, west, then pitch. If you have to remove an insert from a tool you can take a different color Sharpie and mark the cutting edge of the insert to indicate where to position it when remounting (the color on the cutting edge will quickly wear off when next used). With Hunter cutters I use the same method to mark north, but a smaller degree of rotation.
I tend to use a cutter for at least one project, and sometimes more, if they aren't important pieces. If I'm going to rotate/change an insert I tend to start out with the old edge, then change when I'm getting closer to the final cuts. I try to have a low threshold for changing edges. I figure if the insert cost 20, then a change out is a 5 dollar decision. But, I don't only use carbide scrapers, so the final surface may be achieved with another tool, e.g. a NRS. Hence I may use a given carbide edge longer than someone else might choose to do.
One final thought. I just now replaced a square cutter on a tool and I was somewhat dismayed to find that the insert had chipped along the bottom surface where it couldn't be readily seen without removing the insert. From now one I will be removing and inspecting the insert each time it is "rotated" and not just turning it on a loosened screw.