I don't know if the original poster is still reading this forum, but I want to say something anyway.
As a fellow agnostic, I understand the first question, and thought of it many times in the past. "What's the big deal; He's not really dying." Then I thought of what many of the later posters said. It's a lot of pain, and He thought of it and dreaded it the way we would. If we had to have, for example, surgery without an anesthetic, no matter what good purpose it would serve, we would be horrified at the prospect.
The later questions and answers are beyond my comprehension so far. In general, where I've arrived in my thinking is that when there's something that puzzles me, I keep reading the Bible in hopes that it's clarified later. As for the Trinity, I don't have much trouble just accepting it that it can be true, regardless of whether I can totally understand it. I don't even fully understand how my car works.
