He was involved as a "consultant"...but barely had any involvement from what I heard. I read an interview with Kathleen Kennedy who said he was finding it incredibly hard to let go of the Star Wars Universe, but my understanding is that he has been kept well away from anything!
No, that's a totally separate character, Kylo Ren. http://www.empireonline.com/news/story.asp?NID=45203
My mate has heard that Luke is only in it for a very short time towards the end of the movie...which is probably why he's not on the poster.