I am trying to dial in my Flemish strings making (Usually do three bundle). But i need to figure out a few things so any help would be greatly appreciated!

1.  after the string is at the desired lenght (completely stretched and perfect brace height is set) how many twist should there be per inch in a string?

2.  will a 12 strand b-50 string hold up to a 65# recurve?

Hope to here from u all soon! thanks again and good hunting to all!

I read somewhere that the ideal twist is about one per inch. Less is a problem, more is not much of a problem.

12 strand B-50 is OK but at the low end for a 65#. Are you trying to make a lighter/faster string or going for arrow nock fit? I like TS1+ for lighter thinner faster string - its stronger per strand and thinner.

1. after the string is at the desired lenght (completely stretched and perfect brace height is set) how many twist should there be per inch in a string?

I never count.  It's going to vary some, depending on the diameter of the string.

2. will a 12 strand b-50 string hold up to a 65# recurve?

Yes, but it's going to stretch like crazy and retract when you unstring the bow.

I would use 15 or 16 strands on a 65# bow.  As has been said, 12 will stretch quite a bit.