Cant be asked to read all the bullshit here, but here are the answers to your questions. Im not religeous, im just a student so of course I know this.
1. If God is Omnipotent, then why is there evil in the world? I have heard every single justification for this, from free will to the "evil is necessary so goodness an show up by contrast" one. None of them wash with me.
Humans have free will, free will to make our own decisions, when we ate that freaking apple we learned about good and evil. There is evil in the world because some people choose to do evil.
2. If Christ is the Messiah, then why didn't humanity enjoy a better life after he was here? There were still wars, and poverty, and suffering. I don't think most Christians understand the Jewish concept of a "Messiah". That person is supposed to SAVE us. I'm not feeling the saving bit so much.
Jesus saved us by taking away the sin we were born with because of the whole "dont eat that apple!"
3. I don't get what the Holy Spirit is about. A Supreme Being that seems not to have existed before God wanted to knock Mary up and now has no purpose at all.
God, the holy spirit and jesus are the same thing, how wierd that may sound. They are three different aspects of the same thing
4. The notion of a Trinity seems to contradict the first of the Ten Commandments: monotheism. If there is only one God, there cannot be three. It just isn't rational.
Check out the answer for question number 3. Oh and by the way, the ten commandments arent christian unless you are talking about the commandments Jesus gave, but I think you are thinking about Moses.
5. Speaking of rational, thanks for the condemnation of abortion, birth control, sex for Clergy (that paid off so well, didn't it?), people who are not Catholic (or whatever flavor you may be), etc. A special thanks to the "Creationism" nutters who've brought a new age of enlightenment into the classroom.
Dont really see any question here
6. How is it "Christian" to deny food or medical care to a child if their parents won't first agree to convert to your religion? If your religion is so great, won't the people whom you serve eventually get curious about it? Why's it okay to coerce people into relinquishing their culture and their beliefs in favor of yours because you have the economic upper hand?
Its not okay, if any christians are doing that, they arent true christians.
7. If prayer actually works, and God actually listens, isn't it evil to pray for the defeat of a high school football team or the results of a test? Doesn't God expect that you'll only pray for stuff that brings you closer to him?
Dont have a real answer for that, but being selfish is a bad thing, so my guess would be that he puts you on ignore
8. How is it possible to reconcile, in your own mind, all the hatred and aggression undertaken in the name of religion with any message of any major religion? You know that it is wrong. How is it okay to commit Major Evil as long as you invoke God's name?
It isnt okay. Anyone claiming to do evil in God's name, doesnt know a thing about God and will be punished by Jesus on judgement day

Killing isnt accepted, to bad for all the soldiers
9. How can you seriously believe that a man in a red jump suit "tempts" you? Why can't you just accept responsibility for the evil you do? You're human -- no one has to tempt you. You're full of evil, selfish impulses and can only control them through the wonders of social conditioning, like the rest of us.
Are you thinking about santa claus?

Humans are evil or good by nature, we learned about good and evil when they ate that freaking apple. We can choose what to do, some people choose evil and some choose good sometimes. Our dicisions is what we will be judged on at judgement day. So no, nobody tempting us, we decide ourselves.
10. Why do you need a "promise of Heaven" to do what you know is right? Don't you have a conscience? When you do the wrong thing, don't you feel that?
I guess they need a carrot
