Why did he say "Anasos Lech"?
Targum Yonasan: Go to there. Rashi - he was from there.
Radak: It is as if it says 'Ish Anasos, go [to your field].' Anasos was given to the Kohanim (Yehoshua 21:18), and it says "Min ha'Kohanim Asher ba'Anasos" (Yirmeyah 1:1). Similarly "va'Ani Sefilah" (Tehilim 109:4) is like 'va'Ani Ish Sefilah', "Sheker Mezin" (Mishlei 17:4) is like 'Ish Sheker', "Damesek Eliezer" (Bereishis 15:2) is like Ish Damesek.
Kli Yakar citing Mahari: Go to Anasos, to your field, and do not go to and fro. I.e. he will not serve even as a Kohen Hedyot. 1
Even without Shlomo's command, since he once served as Kohen Gadol, he may not serve again as a Hedyot, for we ascend in Kedushah, and do not descend (Yuma 12b)! Surely he was no worse than a Zar, and could do Avodah for which a Zar is Kosher, e.g. Shechitah, flaying and dissecting (Yuma 27a). Now he may not come to the Mikdash, so he cannot do even these. (PF)
Why did he say "Al Sadecha"?
Radak: This is like El Sadecha. Similarly, "ha'Ramasah Al Beiso" (Shmuel I, 2:11, is like El Beiso) and "va'Tispalel Al Hashem" (Shmuel I, 1:10) is like El Hashem.
Why was he Chayav Misah?
Rashi: He rebelled against David's kingship by trying to make Adoniyahu king without David's consent. Radak - it seems that he knew that David wanted Shlomo to reign. However, in any case one who appoints someone else to be king in the king's lifetime, without his permission, is Chayav Misah.
When did he carry the Aron?
Rashi: It is when David fled from Avshalom.
What affliction did he suffer?
Rashi: "Ki Amru ha'Am Ra'ev v'Ayef v'Tzamei ba'Midbar" (Shmuel II, 17:29, when David fled Avshalom). Radak - and also when David fled Sha'ul.
