Well they may not use the phrase “chicken” in the first one (I honestly can’t remember if they do) but certainly there’s the whole “I care too much about what people might think of me” thing, as evidenced in Marty’s reluctance to show his songs to anybody and George’s reluctance to let anybody read his stories. Surely we can use this as a precedent for “chicken”?
Oh come on, this is just a riff on the ol’ “History repeats itself” meme.
Okay, this I agree with you on. 
I really don’t think it noticed. If it didn’t see it long before it hit in order to stop, it wouldn’t have seen it after it destroyed it. The train plowed through that thing like it was made of paper. If you recall, the Doc even mentioned that the DeLorean was not particularly sturdy and would not survive a battle with even Biff’s old car.
I have over 3,000 DVDs in my collection, mostly in case I ever MIGHT want to watch them again. The Back to the Future trilogy is a set that I do enjoy every several months when company wants to watch them. They’re fun to watch, and it’s not so much about any pretense at plausability but just the comical disconnects between “future me” and “past me”. Good acting, hammy as it is, carries it off well.
The first was inventive and funny. The second was darker, and admittedly a connector to the third one. You could actually watch #3 and never really need #2 to enjoy it. Still, #2 plays up the future/past meeting/disconnect more so than the first. As I said, if you relax and watch it for the fun, it’s enjoyable. Try to analyze it too much, and it would be irritating.
Go ahead and watch all three, from the beginning. They tend to segue into each other and they are fun to watch. And #3 resolves Marty McFly’s predicament in middle age from #2, as well as provide the overall Moral of the Story from all three.