Kivas, no, no I didn't do any staining what-so-ever until the belt was completely made.
Honestly, about the trimming, I'm someone who likes to cut excess and trim the excess later on rather than make the mistake of cutting something too short...that's it. As long as you glue that first middle strand right on the line and tuck in your other strand tight to that, then you could get away with less width. I also found the extra width helpful in giving me a larger piece to work with and when spreading the glue around cuz I didn't have to worry about smearing it off the leather.
Also, I used some very flexible backing that is about 1/16" thick (maybe even a tad less) and I glued the strands to the "fuzzy" side so that when I wrapped my ends around the finished side showed and because I figured the glue would stick better to the rougher surface.
Also keep in mind that I cut my strands with 4" extra when I could have gone with 2" extra and gotten another strand for 22 total. But, I didn't need 22 so I didn't worry about it, but a taller guy who wants more strands might. As long as you find the exact center of your strands when your gluing them down in the center, and be sure to place that on your center marker line, you're good to go. But I would leave some excess for trimming so you can get that straight edge on the ends.
I also tugged on the ends of each strand before I found the center in case any had shrunk a little.
Oh, and when your cord first comes off the spool, it will be very coiled, so I took mine off the spool and laid it in the sun for a couple days at the side of the house and then for a few more days in the garage to help it relax a little and take out some of those bends.
Anything else just let me know. I'm happy to help.
Cruzer