+1 on this. If you're considering a 2 degree slackening of the STA and asking if that would be better, then you need to understand more about your particular fit before you start making a frame to fit it.OK.
I think maybe a halt might be wise here. The reason is that there is a need to digest the info a bit, but also suggest more info might be needed to not confuse the original request. Progress has been made, but a proper fitting with an experienced builder might be a good direction to go, then, a purpose built frame can be successful. The right elements exist here, but a personal fit would really be needed to go forward on.
Sure, but if you don't know what you want, why not at least put it somewhere in the middle to give you the most range in both directions to experiment with? If most of his range is going to come from shoving things backwards, at his weight (and with a 27.2 seatpost) that's not where you'd really want to end up. There's certainly nothing gained by the steeper seat tube unless he has odd proportions.Is it a good idea to know what your saddle setback needs to be and design for it? Of course! Is it the end of the world if you miss by a degree or two? No.