Thanks for sharing your Nikon System with us. I use three Nikon F2 bodies. One body I have used since 1971. I never used Nikkormat bodies because they never felt good in my hands and I did not like their ergonomics. Like you, I have the 135mm f/3.5 and the 105mm f/2.5 telephoto lenses. Great lenses. Why do you not have any wide-angle lenses or zoom lenses?
Nikon manufactured an accessory shoe for the FTn. it would sit right on top of the viewfinder and is held in place by the eyepiece. It works okay. I haven't really used flash with my Nikkormat partly because I can't very well dial in my flash exposure on film as I can with digital, and partly because the x-sync terminal on mine doesn't work.