1. No, there are sightings all over the world.
2. No.
3. A lot of the experts on the matter believe they bury their dead. The American government has bodies/knows all about it.
4. Plenty of scientists are out there looking.
5. They couldn't give a definite answer as to what the samples were, pretty close to human though, but not quite.
eta. also worth noting that the mountain gorilla wasn't discovered till 1902.