I'm shooting a 68" osage bow, and I use the fistmele for measuring brace height. This works out to 6" (15cm), which is perfect for keeping my fletchings off the bow. As for the wrist slap, get an arm guard. At 15cm brace height the string still slaps my arm, so I always shoot with a good arm guard.
As far as arrow spine is concerned, it is usually a good idea to go with something a little under your draw weight when matching arrows toa self bow. Also, for every inch you cut your arrows above or below 28" you need to subtract or add 5# spine respectively. To be perfectly honest, I have never spined my arrow shafts. I make my arrows from Red Osier shoots, so I just experimented until I found what worked with my bow, then I made everything else to match that. With a little practice, it isn't hard to do. Besides, a spine tester is an unnecessary expense, unless you make your own.