1) Hashem did not tell Avraham where to go; he just told him "lech lecha... el ha'aretz asher areka." Don't worry -- keep walking around and I'll let you know when you get there. Why didn't Hashem just say straight away to go to Eretz Yisrael?
Rashi writes that Hashem wanted to increase Avraham's chibuv mitzvah and his schar. When you don't know where you are going, there is a constant sense of anticipation -- "Is this the place Hashem wants me to be? Is this where I will fulfill my mission?"
Sefas Emes explains that in effect Hashem did reveal to Avraham to go to Eretz Yisrael because this is what Eretz Yisrael is all about. When you think of some neighborhoods you think of the good shopping, you may think of the close by transportation, you may like the restaurants, etc. That's what those places are all about. Eretz Yisrael is the place where a person can think about "Is this where Hashem wants me to be? Is this where I can fulfill my mission?" Eretz Yisrael is the place where a person can live in constant anticipation of coming closer to Hashem, of greater chibuv mitzvah.
When a kid of 17 or 18 goes to yeshiva or seminary in Eretz Yisrael, the reason they have such a productive year of growth is not because that's naturally what happens when adolescents spend a year away from home in any foreign country. It's because the nature of Eretz Yisrael is growth. There is always an "asher ar'eka," a sense that there is something more to see, something more to learn and discover. You cannot exhaust the wonders of Eretz Yisrael.
For those of us unfortunately still in chu"l, Shabbos is in time what Eretz Yisrael is in place. Shem m'Shmuel (5675):
ויש לומר עוד היות ידוע שהתורה היא נצחית ומאמר הש"י לאברהם לך לך מארצך וממולדתך ומבית אביך, עודנה כמו חי עומד וקורא בקול לנשמת ישראל בכל ערב שבת לך לך וגו' לעשות שלשה הבדלים מימי החול לשבת לקיים את הארץ וגו' שבשבת זוכין לבחי' ארץ ישראל כמו שהגיד כ"ק אבי אדומו"ר זצללה"ה שארץ ישראל שהיא האוקלים אמצעי השביעי מקביל לשבת שהוא יום השביעי ואמצעי תלת יומי קמי שבתא ותלת יומא בתר שבתא עכ"ד ועם זה מתקיים נמי אשר אראך שבשבת זוכין לבחי' ראי', וזה ענין אמרם ז"ל פסיעה גסה נוטלת מאור עיניו של אדם ומהדר לי' בקדושא דבי שמשא, וזה ענין נר של שבת וזה שיסד האריז"ל בזמירות שלו נזמן לה השתא בפתורא חדתא ובמנרתא טבתא דנהרין על רישין, ועוד שם חדי סגי ייתי ועל חדא תרתי נהורא לה ימטי וברכאן דנפישין:
2) Someone commented that in my discussion of the Rosh by birchas eirusin I never explained how the Rambam, who holds that birchas eirusin is a birchas ha'mitzvah, answers the question of why the nusach ha'bracha is the lenghty "asher asar lanu es ha'arayos..." etc. When you do shechita (the Rosh's point of comparison), you don't say "asher asar lanu neveila..." etc. Why is birchas eirusin different?
The Achronim ask why it is that Avraham, who Chazal tell us observed the entire Torah, did not fulfill the mitzvah of milah before it was given. The Brisker Rav answers that by definition there has to be an orlah in order to fulfill the mitzvah of milah. Until Hashem gave the command of milah, there was no orlah -- there was a physical piece of skin, but it had no legal status as something that has to be removed. So too with respect to kiddushin -- the mitzvah of kiddushin not only created a process by which Klal Yisrael would effect ishus, but it also created a whole new set of arayos categories that do not exist for bnei Noach. Therefore, birchas eirusin does not just talk about the mitzvah of being mekadesh, but also speaks about the "asher asar lanu es ha'arayos..."
R' Asher Weiss in Minchas Asher points out that you can make this chakira by many mitzvos. Is it the mitzvah of hafrashas terumah that creates the status of tevel, or is tevel an independent issur? Is it the mitzvah of shechita that defines what neveila is, or is it an independent issur (we see from the Rosh that the two do not go hand in hand.)
With respect to the question of why Avraham did not do milah before commanded, R' Asher Weiss suggests (as do others) that the nature of the mitzvah is bris, creating a covenant. It takes two parties to make a bris, so Avraham had to wait for Hashem's command before doing milah.