1-4 look correct to me.
for #5, you are correct that to come is not a prepositional phrase because there is no object. If I were you, I'd leave it alone and keep the one next it. all others look correct.
1. the main point
2. feudalism
3. feudalism
Ronald Mcnair , an American physicist, died during the launch of the Space Shuttle Challenge. McNair is an inspiration to many young NASA astronauts.
you can say "much apreciated" or jus "thanks!" lol
