I'm personally highly skeptical of the claims he's making—or that extraterrestrials are here in any capacity—but to take a stab at your questions:

- the folks who do believe in UFOs would say these crashes happen worldwide, but it's countries like the US/Russia who use their influence to swoop in, recover the pieces and then mount a coverup.

- UFOs have been sighted over urban areas, although it's rarer. If I were a UFO pilot, I'd probably avoid cities for the same reason the USAF doesn't fly classified aircraft over urban areas either (at least during the day)

I don't know what his angle is here—fame, mental issues, a genuine belief that he's onto something. I'll admit the recent focus on these things has aroused my curiosity, but like I said, aliens aren't at the top of my "credible explanations" list.