You bring up some very deep and complicated issues, many of which I don't believe I can adequately address in one sitting. I'll start with your #1 under "paradox." The same law applies after Jesus as before Jesus. Before Jesus was on Earth, Jews had to sacrifice animals and burnt offerings as atonement for their sins. So Adam and Eve (if they existed) would have been taught the law by God and would know atone for their sins in accordance to his law, and that would be how they are in heaven. As for after Jesus, He was the "perfect offering" that atoned for all sins for everyone who believes His death covers their sins.