I haven't seen anyone give an answer about how affixes are chosen from the list of available ones. Until I did the following, I assumed they chose the affixes from all of the possible ones, then decided whether it was the most powerful version or a lower one, and then if it were a range of values, roll the final result. But I no longer think it is that simple.
Lets assume you're crafting armor with 6 affixes and there are 12 possible choice not counting stats, plus 4 stats plus 6 doublestats (str/vit, or somesuch)
The number of possible items without a doublestat affix (one affix that provides two stats) would be:
16!/(10! x 6!)
The number of possible items with one doublestat and 5 of the other 14 affixes (12 plus the two stats not in the double stat) would be:
6*14!/(9! x 5!) = 6*10*6*14!/(10! x 6!) = 1.5*16!/(10! x 6!)
so 60% of all the 6 affix items would have a doublestat if they were equally likely.
This number is so out of keeping with what I've observed that I've either screwed up my math, made a really false assumption, or the affixes aren't equally likely.
Which is it?
My ultimate goal is to set up a spreadsheet that calculates how much a 4, 5 or 6 affix ilvl62 mighty belt (I'm also interested in boots and helms) is worth on average if I were to make hundreds. If I've missed anyone elses work on theorycrafting the odds of rare item creations, I'd love to know about it.