From when is "Galuseinu"?
Malbim: It is Galus Yehoyachin. He was exiled 11 years before the Churban.
How can it be "b'Rosh Hashanah b'Asor la'Chodesh"?
Rashi (citing Erchin 12a): Rosh Hashanah is on the 10th of the month in Yovel 1 (Yom Kipur is like Rosh Hashanah). The Bayis was destroyed in the 36th year of Yovel, which began in Yoshiyah's 18th year. The next Yovel should have been in another 14 years 2 , in the 25th year from Yechanyah, who was exiled in the 26th year of Yovel. There were 14 years of Yoshiyah from his 18th year until his 31st (final) year, and 11 years of Yehoyakim.
Radak: The vision of returning from Galus in the days of Mashi'ach and building the city and Mikdash was on Yom Kipur of Yovel, when slaves go free. This shows that Hashem will pardon Yisrael's sin and not mention it again.
Radak (here and 1:1): Yechezkel had a vision of the honor leaving Yerushalayim 30 years after the Sefer was found, five years after Galus Yechanyah. There remained 20 years until Yovel ? six of Tzidkiyah, and 14 after the Churban.
Why does it say that "Yad Hashem" was on him?
Rashi: It is Hashem's power to force him to go Bal Korcho (against his will).
Malbim: This is motivating the Navi to exalted matters and awesome visions.
Where is "Shamah"?
Rashi: It is the city that was stricken ? Yerushalayim. That year, He showed to him the future Beis ha'Mikdash.
