Hi, I'm going to answer as if you were talking about yourself here, even if it's not clear in your question.
There are lots of ways to be asexual. Some won't feel any will to have sex but will still engage in it because it doesn't bother them particularly (for instance if it's important for their partner in their relationship or because they like the intimacy and closeness with their partner but not the act itself in particular), some will be repulsed by sex and won't engage in any kind of sexual stuff.. Some won't masturbate but others will (for instance to release their sex drive which is just mechanical) etc.
The important thing for me is to be wary of owning a term you're not sure about. If you're not sure you're ace, then don't use it to describe yourself / your experience. You have a right to be in questionning, and that's totally legitimate for you to be. In the meantime, you can go to some asexuality themed forums (like Aven) to read some stories, and get a better idea of how broad asexuality can be, and how exactly you can situate yourself on the spectrum of (a)sexuality :)
Yes, you absolutely can!
I'm asexual too. :)
If you aren't sexually attracted then you are - by definition - asexual, and that doesn't change based on your reading preferences!
A lot of people have a lot of words to describe where they fit on the spectrum of asexuality. If you enjoy finding which words fit you most, awesome! Explore! If you'd rather not dive in too deep, I understand and - one Ace to another - give you permission to both love your dirty fanfics and embrace your Ace! ;)
You are valid and perfectly okay!
I'm so glad you exist!