But your advises are decent.

Don't over explain, don't be creepy and keep in mind it's completely individual and there are no rules to it.

Some girls like other people playing with their hair - guys or girls

Some would have some worries if a guy is asking, but if you're likeable enough, you will get a permission

Some will think it's too weird, so don't be pushy and just let it go

Some just hate people other than their hairdresser touching their hair, and it's nothing personal.

Regardless of the girl's type, as said before, always compliment in the most nonchalant way on their hair. And please don't be awkward about it. "your hair looks really nice/soft" is much better than a "sexy" comment which can be misinterpreted.

And BTW, some girls know (their) hair is attractive and are aware of hair fetish, and either don't care or even likes it.

So just approach with care and feel the atmosphere.