Juice Box, why don't you just play Dragon's Dogma instead of spending all of your free time thinking about this?
1) I think that our purpose in life is to make our lives as enjoyable as can be. This is human nature; it's impossible
not to do what you want, no matter how hard you try. Even if you want to do something that you don't want to do just to spite my theory, you want to prove me wrong, so you want to do whatever painful, thing you're doing to prove something. Even if you're blackmailed to kill someone, you want to kill that person just because the outcome of the blackmail is worse. We strive to make our lives as fun or as pleasant as we are able because humans want to have fun. I personally find enjoyment in being productive and useful, so I want to make video games that can make other people's lives that much more enjoyable.
2) Humanity on earth is scientifically bound to end, along with the rest of the universe. However, when you say ultimate, I imagine that you mean the true, final fate, behind our current lives. If there is an afterlife, I think (or hope) that it will have qualities beyond your comprehension that make eternal life worth living, as opposed to the stories you hear about people with immortality that don't want it and yearn for the freedom of release. I believe in things beyond our understanding mostly because I want there to be far more to discover after current life, yet I haven't got any evidence.
3) I believe my answer to 2 answered this one.
4) If the world is to eventually cease to exist and plunge us into an infinite afterlife, it would say a lot about life's enjoyment. Perhaps this infinite afterlife will give humans some way to forever seek happiness without feeling like it's futile, but still make them earn more the way our current lives require our effort to become better.
5 is a scientific answer. It would be best explained from some credible scientific source.