What did Bil'am mean when he said "Hineni Holech l'Ami" (and not 'li'Mekomi')?
Rashi: He meant that his status had been lowered to the point that he was on a par with the rest of his countrymen.
What advice did he offer Balak?
Rashi (from Sanhedrin, 106a): He advised him 1 that, since the G-d of Yisrael hates Zenus, [Targum Yonason - they should set up shops manned by prostitutes selling food and drink at cut prices. 2 Yisrael will then eat and drink and become inebriated. be intimate with them and deny their G-d. 3 As a result, in no time at all, they will be handed over to Balak, and many of them will die].
Ramban: He was telling Balak the plan that Hashem had in store regarding what Yisrael would do to Mo'av in the days of Mashi'ach.
Da'as Zekenim, Hadar Zekenim (1): This that you fear the nation opposite you
Rashi: We know that Bil'am was the one to give this advice from 31:16.
Sanhedrin, 106a: Old harlots sold linen garments outside for their true value, and young harlots sold inside for less. Yisrael ate, drank and were merry, and went to the market. After two or three sales, the young ones said 'you are like family. Take for free', and gave to them Amoni wine (before Chachamim forbade Nochri wine). The Yisrael drank, his Yetzer was aroused, and she consented to Bi'ah only after he excretes in front of Ba'al Pe'or; afterwards, she stipulated that he must deny the entire Torah of Moshe - "va'Yinazru la'Boshes va'Yihyu Shikutzim k'Ahavam" (Hoshe'a 9:10).
What does the latter half of the Pasuk mean?
Ramban #1 (citing Rashi): Bil'am actually had in mind to inform Balak that, in the days of Mashi'ach, Mo'av was destined to fall into the hands of Yisrael. In the meantime however, he advised him what Mo'av was able to do to cause havoc to Yisrael. 1
Targum Onkelos: Bil'am was telling Balak that in the days of Mashi'ach, Mo'av is destined to fall into the hands of Yisrael.
Targum Yonasan: The advice concerned the present. Eventually however (in the time of Mashi'ach), Mo'av was destined to fall into the hands of Yisrael.
Ramban (25:18): Bil'am concocted the plan in conjunction with the elders of Midyan.
Why did he say "Asher Ya'aseh ha'Am ha'Zeh l'Amcha"? He should have said oppositely, for he counseled Mo'av to make Yisrael stumble in Zenus!
Rashi (Sanhedrin 106a) #1: Bil'am did not want it to sound as if Mo'av needs to take counsel against Yisrael.
Rashi (Sanhedrin 106a) #2: The Torah did not want to it sound as if Yisrael was cursed.
Da'as Zekenim: The coming verses tell what Yisrael will do to your nation. (It is not part of his counsel.)
Why did he say "v'Atah"?
Michtav me'Eliyahu (1, p. 236)