My questions about Prometheus

I've just seen Prometheus, and I was somewhat dissapointed by some parts of the plot that didn't seem to make sense. I don't want to dismiss the movie (it was entertaining), and I don't expect a perfect plot, but if I can find a plausible interpretation of some questions, I guess my dissatisfaction would decrease, so I'd like to know if some of you have found some way to make sense, or if you would agree with me that they don't make sense.
(1) Why do the Engineers "invite" (with the drawings in several cultures) humans to LV233, which turns to be a military base where they prepare a bioweapon against humans?
(2) Why does the first Engineer kill himself? If his goal was to offer his DNA to create life on Earth, couldn't he have done this without killing himself?
(3) Why do the Engineers first create and contact and "invite" humans, and later try to exterminate them with a bioweapon?
(4) Why do the Engineers have a mural with an Alien?
(5) Why does David infect Holloway with the black substance?
(6) If something went wrong 2000 years ago and some mutated lifeforms killed almost all Engineers in LV233, why there're not more mutated lifeforms in LV233?
(7) If Engineers had a plan to exterminate humans and their bioweapon backfired 2000 years ago, why the other Engineers did nothing since then, in order to rescue the survivors in LV233, or continue their plan?
I've found much more examples like these. What do you think? Can you make sense of them?