What does the first half of the Pasuk mean?
Rashi: It means that there will be so much grain to thresh (around Shavu'os time) that they will still be busy with it when the time comes to harvest the grapes (in Tishrei), and the grape harvest will last until the time to seed.
What are the implications of "Va''achaltem Lachmechem la'Sova"?
Which is of itself, a healthy thing to do. See Oznayim la'Torah. Moshav Zekenim
If you will eat little and be satisfied, what is the point of all the grain and wine?
Rashbam (10): You will sell it to other (Seforno 10; Shir Ma'on
Since there will be such abundance of food, obviously you will eat to satiation! Why must the Torah say this?
Moshav Zekenim: One might have thought that you will be so distracted with gathering the harvest that you will not have time to eat. Therefore, it teaches that you will eat a little and be satiated, like Rashi said.
Shir Ma'on: Most rich people are unhealthy due to overeating. Hashem will enable you to resist temptation; you will eat only to satiation.
Rashi writes that Batzir (the grape harvest) will last until Zera (the time to seed). What is the Brachah? Batzir is in Tishrei, Zera is Tishrei and Cheshvan (Bava Metzi'a 106b)!
Riva: All of Tishrei is Batzir, i.e. if one did not do so earlier, all of Tishrei is proper for Batzir. Zera begins in Cheshvan, 1 The Brachah is, even if one begins Batzir at the beginning of Tishrei, it will last until Cheshvan.
This is like R. Shimon. R. Shimon ben Gamliel says that Zera begins in the middle of Tishrei; R. Yehudah says, at the beginning of Tishrei. How can we answer for R. Yehudah?! Perhaps just like they argue about the time of Zera, they argue about the time of Batzir. (PF)