The answers to your questions depend on location. Different regions and even different streets in the same city have different etiquettes.

On the Hudson River Greenway, there isn't a lot of calling out "on your left" or whatever. Those who do it to me startle me, because they're going a lot faster than I am, so it's worse than useless.

I rode with a friend on another trail, and his practice was to call out "hello" in a glad-to-see-you kind of voice. I think it was a bit of theater, but I think it's a good thing. It wipes away the tendency for the person being passed to think that the passing person is annoyed at having to share the space.

Flashing or steady lights are not meaningful except whatever the user prefers. In fact, it may mean even less than nothing, because some lights are used very thoughtlessly. One example is the strobe that flashes two or three times a second and is intensely bright and pointing straight ahead, on a bike path. That person is either oblivious to what it's like to encounter his light, or he's a jerk. Another example is a person with a red light in front and a white light in back. Maybe he thinks it keeps us on our toes. More likely, he hasn't thought about what the convention is and why conventions are useful things. But I really don't know.

Riding against traffic is super dumb. If you're still doing it, please stop. When I encounter someone doing it, there's no way for me to predict what he's going to do, so I try to keep a steady course, expecting him to dart in any direction without warning. If someone is going to act like a child, I'll treat them like one.