I think what he was trying to say is that you need someone else to teach you in a dream. You cant teach yourself new knowledge without having first taught yourself the knowledge.

I guess its possible but i think its quite pointless to discuss what other things you can achieve with the device. You can hook up an entire population to the device but thats not what the movie is about. And more importantly, the stuff in the film is not to be taken too literally. Like all films there bound to be a level of ambiguity and ridiculousness. Its all fake but you just go along with it.