I can give you my personal responses to your questions, which should get your going in the right direction. You can research from that point on.
Blue whales are, in general, eaten by creatures much smaller than themselves.
Orca whales are known to at least occasionally kill and partially devour blue whales. Your question about interactions is too broad for me to answer fully. During its lifetime, a blue whale probably encounters tens of thousands of species of animals in the ocean, many of which it interacts with in some way. Blue whales have been seen in the company of many species of dolphins and other whales, including orca. I have personally seen them near minke, fin and humpback whales, Risso's and bottlenose dolphins, and probably some other animals I have forgotten.