Hello Josh.
First, it is possible to have a relationship with either Dawn Star or Silk Fox if you follow the correct dialogues with them and are using a male character (rumors also say you can get both at once, but I haven't been able to accomplish that yet). To do this, you should make a point of talking to them every time they have a yellow arrow above their heads and always selecting the option that causes your character model to make a smiley face when you select it. As well, it is possible to have a relationship with Sky if you are a female character, although rumor has it that Sky will have a relationship with either gender, as will silk fox.
Secondly, No. There is no actual sex. If you have successfully acheived and nurtured a relationship with one of the NPC's, then after you have been revived and have gathered at Dirge with your friends, you can initiate a romantic cutscene by talking to Dawn Star, Silk Fox, or Sky outside your tent before the imperial army attacks, however, the extent of the "romance" is some mushy talk and a kiss before a fadeout.
Thirdly, unfortunately I do not have the Limited Edition, and so I can't help you there. Good luck and have fun enjoying this totally awesome game, and if you can, please reply with a list of where limited edition differs from regular edition.
=^x^= ryv