Personally Ishmael, I wouldn't have the edging but you could easily try it to see if you like it. It gives it a different look and could look pretty good with your cut on a black bike.
Interesting about the rusting. The bits I cut off got damp and rusted a little along the cut edge overnight but the bit on the bike hasn't. I was going to run a candle or something like that along the edge to give it sort of a coating. It seems that not having water sit on the edge means it will be OK. Not sure what others have found over time.
As for a template, don't see how that would be any easier as it would involved measuring and guessing just to line it up. I cut mine more or less like Mitch's too. I measured under the claw from the top of each filter to the bottom of the claw - they're different. Then took the claw off, turned it over and marked the inside, starting with the centre of each pod and then drew a line more or less following the line of the bottom edge. I initially drew my line about an inch below the top of each filter. I marked and cut from the inside because it's very easy to slip with the cutter and leave marks on the chrome. I started taking less than I wanted but it's easier to take off a bit more than to put it back on! Took me three goes and I've and finished up with it about 1/4 inch above each filter! The back filter is still touch the cut edge so I need to take a little more off there.