You write it like adult sites were something completely different from "normal" sites. All blackhat techniques that works for "normal" sites works the same in adult, its just harder to use these techniques, because most websites does not want to to link to adult sites, so its much harder to get services for adult or so, but in my opinion its still best to do the work by yourself. Services usually sucks and bought links are dangerous for long term projects, because one day, google will find out.
Indeed - which is why it's harder to work on adult sites as many outlets are "blocked" for you.
I'm aware of the risks of using any paid links / blackhat techniques and it's sites I'm willing to "sacrifice" for this purpose - short / medium term success is ok with me
Buy SAPE for "good links" and spam for "diversity".
There's also some sort of adult "private" blog network here on BHW but the domains are crap and probably won't get you anywhere.