Haven't read all of this yet.... a consideration is whether you are going to sing in your natural voice or in a flat-tone-colored oldtimey way, and where on the scale your voice breaks and has trouble holding steady in tone color. I wish I could remember what my voice did at Debby McClatchy's workshop on oldtime singing. Try singing along with some stuff in the style you will use, and then see what keys worked best?

~S~