Thank you all for your help, it all sounds so complicated I'll need to read through your posts and check the books at the same time LOL.
I do understand that the dreamworld is an alternate reality and the idea of Inception style powers is actually not feasible (the film is based on the idea that you enter a person's mind when you enter a dream, a whole different concept whaich enables you to phisically find memories and info in the dream, like documents, and you don't need to use telepathy at all).
I think I understood how the concept of +30 roll works for telepathy, my roll must be +30 compared to the victim's MD+EGO (after I have already defeated him on MDCV, otherwise the attack has no effect: just like any punch/shot, my OCV against his DCV and action roll).
One question, is the victim's MD always on the same level? I mean, from a realistic point of view a person's mental defenses should be lower doing sleep or other situations ("hot" ones for example). Is that so or not?