Straight and simple, 2 question arises:
1) if I use only prehensile hair during my attack, do I get iterative natural attacks due to high bab?
2) if I spellstrike vampiric touch and I kill the target, let's say I do 40 damage via vampiric touch and like 15 via weapon and stuff, and the target has, let's say, 42 hp total (including her con score) do I get 40 or 27 temporary hp?
1) No, in general you don't get iterative attacks with a single natural weapon. You get one attack per natural weapon, regardless of BAB. That's one major flaw with trying to make a build based on Prehensile Hair. And since it's a secondary natural weapon, if you ever get any other natural weapons the hair will be penalized, so you can't add other attacks that way.
I've tried various ways to make a good build around prehensile hair, but there are lots of problems with it, and despite the initial appeal and temptation to try to make it work, it seems like there will always be a better way to accomplish similar things some other way. The hex can be a nice addition to pick up for a witch or hexcrafter, it's always nice to have an extra hands free attack, do some attacks of opportunity at reach, or deliver touch spells at reach, but it works better as just a minor add-on rather than a core feature that you try to tailor your build around.
2) Good question. You're essentially asking which comes first in a spellstrike, the spell effect or the weapon damage? It doesn't seem clear to me from the spellstrike description. Since it isn't clear, if I were DM, I might let you choose the order, but maybe someone else can give you a more definitive answer.
Wow, really quick, thanks. Natural weapons argument is always a pain when you come down to details. As for vampiric touch, I'll ask to the DM, since it's not defined. ..
Dude, reread the rules. It specifically says you don't get extra attacks from a high BAB UNLESS you only have a single natural attack that can be used.
Please quote that rule then, because I think you're the one who is mistaken. All it says is that if you only have one natural attack it is treated as primary, not secondary, so you get your full attack bonus and 1 and a half strength bonus. Every interpretation I've looked up about the rules says that you never get iterative attacks with a single natural weapon. If you know better, please quote your source, because it's far from as simple as "dude, reread the rules".