Hi Lucky13, whatcha need to know? Been a bit busy with my Wee Walter (LOL) but I'm still available for any questions you might have. Mostly I have Osprey stuff so far, and a few other books for paints, and a couple of pics of Oesau's myriad #13s.
Oddly enough, 13 is a big part of my life too. The number, at least. Hubby's birthday is July 13, and my son was born at 3:13 p.m. on the 20th of June '08 (was due on Oesau's birthday, but no matter how much I squawked at the docs they wouldn't let me go that far. haa haa)
I do know from what I've read in my research (which is still ongoing, even though it's a bit daunting at times) that he really didn't like kill marks on his plane at all, and was a fan of the color green, which wasn't a "regulation" color from what I've read/studied; and he also hated the F series 109s as well, refusing to fly them until no more parts were available for his Emil.
As to WHEN he started using the number 13? Still working on that. Most pilots, at least from what I've found out, would put that number on as an "up yours" to the fates. Kind of a superstitious thing, 13 being generally seen as unlucky.
The superstitious stuff was really prevalent in WWI - Lothar von Richthofen actually had a FEAR of the #13, having been wounded, at least to his accounts, on the 13th every single time (I think it was actually the 12th on one occasion, memory fails me, I call mombrains as the excuse!)
About the most "well-known" 13-er was Pritzi Baer, yep. But he also flew Red 23 as well.