What is the meaning of "Acharecha Binyamin ba'Amamecha"?
Rashi #1: After [Yehoshua], Hashem will establish Sha'ul from Binyamin to finish off Amalek, and make Amalek like Omemos (extinguished) coals.
Rashi #2: Ba'Amamecha hints to the 200,000 soldiers with whom Sha'ul came against Amalek.
Radak: The suffix Chaf (after you) is as if he address) Efrayim; your nation addresses Binyamin.
Malbim: After you (Ehud) went your Shevet Binyamin.
What is the meaning of "Mini Efrayim Sharsham ba'Amalek"?
Rashi: From 1 Efrayim came the root - Yehoshua Bin Nun weakened Amalek via the sword. This is connected to the above; Hashem established Yehoshua to defeat Amalek.
Malbim: Mini Efrayim are Adirim (verse 13) who went with Ehud. Sharshu (they uprooted) Amalek, who was with Mo'av (3:13).
Radak: The Yud at the end of Mini is extra. Yehoshua is the root of Efrayim and its Nasi.
What is the meaning of "Mini Machir Efrayim Sharsham ba'Amalek"?
Rashi: These are great officers who conquered the Emori - "Shishim Ir Kol Chavel Argov" that Ya'ir conquered (Devarim 3:4,14).
Radak: People came even from Machir in Ever ha'Yarden, and even leaders and Chachamim, and all the more so other people!
Malbim: The ones who came to this war were not warriors, They were Chachamim from Machir, and from Zevulun, those who wield the quill, and not a shield and sword!
Who are Moshchim b'Shevet Sofer?
Radak: They are Chachamim and scribes.
Malbim: Refer to 5:14:3:3.