I think you can but you might want to check their Terms of Service first. I'm pretty sure you can't upload any nudity however.
You probably can, but I wouldn't do it. It could easily invite unsavory types to mess around with your account and they might ban you if your material is too edgy.
I don´t think that you can. I hade seen same adults profile, but I guess that twitter doesn´t allow that. . Check Terms and Services.