Parshat Lech L'cha: To me, this makes no sense

You can read the basics here.

Why did HaShem choose Avram? No reason is given in Genesis, chapter 12, verses 1-3, though the rabbis have certainly created some fine midrashim (rabbinical interpretive stories) to try to explain this choice.

• Sunday, November 6, 2011 update: My husband has the rather interesting theory that gaps were left in the Torah deliberately, to encourage us to come up with our own explanations.

Why did HaShem insist on this weird sacrifice (Genesis, chapter 15)? What was the point of killing those animals, since Avram wasn't going to eat them?

• Sunday, November 6, 2011 update: The darshan (?--person who gave the d'var Torah/word of Torah/Bible discussion) yesterday at my favorite egalitarian synagogue in Manhattan said that this was a typical way of establishing a treaty in the ancient Near East, but that the unusual part is that only G-d (or G-d's representative fire and smoke), walked between the parts.

Why did HaShem not bother telling Sarai/Sarah that she was going to have a child before she offered Hagar to Avram/Avraham as a surrogate mother? Did HaShem want to create strife?