An advise, if you think on limits, they´ll be there. You´ll wake up or nothing will happen because you are not sure enough. In LD´s are no limits. If the person has never expierenced sex p. e. your mind will give you the sensations. Maybe it wont be such like sex IRL but I think it´ll be good also (maybe better as in Real^^)
Dont think about the limits think about the possibilities!