A75
a) RAW, no, it doesn't specify that your unarmed strike is a 2H weapon now, however, if you use only your unarmed strike without TWFing or something, it is already treated that way.
b)RAW, stacks.
c)It does say while using this style, meaning the style feat must be in use. So the conditions are:
-Ignoring difficult terrain on a charge
-Charge through allies
-Using your increased damage bonus on your unarmed strike
a) But a monk's unarmed strike is a natural weapon, is it not? And it's certainly "primary." Power Attack says:
"This bonus to damage is increased by half (+50%) if you are making an attack with a two-handed weapon, a one handed weapon using two hands,
or a primary natural weapon that adds 1-1/2 times your Strength modifier on damage rolls."
b) Cool! Glad to know a major chunck of the Style feat doesn't just go obsolete.
c) I disagree on what "using this style" means. I think it merely means being IN the style stance, since you have to actually spend a swift to initiate it, you don't get to just walk into a fight with it on, like ToB stances. Further, the Snake Fang feat lets you AoO someone who misses you and, if that hits, spend an immediate action to attack them again. it says you must be using the Snake Style feat to do this. But the only things Snake Style gives you are +2 sense motive and the ability to use sense motive as an immediate action to negate a hit. If using a style meant needing to use all of it, snake fang's immediate action attack could never be used! More related to the point, the 3rd feat in the Dragon tree is Dragon Roar, which says: "While using Dragon Style, as a standard action you can expend two Stunning Fist attempts to unleash a concussive roar in a 15-foot cone." If you're not using Dragon Style unless you're charging through allies and difficult terrain and attacking with your unarmed strike, Dragon Roar is beyond impossible to ever use.