I think the most interesting point you raised there, is that even though they will probably be relatively peaceful, they will almost definitely have different values from us. So their version of peaceful, might not tally with ours.
I love thinking about this stuff, I really hope that intelligent alien life is discovered in my lifetime.
While I doubt things will go smoothly with every species we encounter, I am pretty confident that we have allies out there watching us, whether we will meet them in our lifetimes....that I'm not sure. I think they are probably waiting for us to stop fighting each other before they show themselves....