?B?nei lo ba?Zeh Shiv?ah Mizb?chos?. Why specifically ?ba?Zeh? (here)?
Seforno: Because it was a point from where he would be able to see Yisrael.
What is the significance of the seven bulls and the seven rams on seven Mizb'chos?
Ibn Ezra 1 : 'The number seven is prominent in the days of the week, in the months and in the years; in the seven rams of the Olah (of most Musaf offerings) and the seven sprinklings (on Yom Kipur). 2
Ba'al ha'Turim: It was customary for Nochrim to bring seven of each species as sacrifices, 3 corresponding to the seven Mitzvos B'nei No'ach.
Presenting one of the deep secrets of Torah.
It also corresponds to the seven Sefiros - Chesed, Gevurah, Tiferes, Netzach, Hod, Y'sod and Malchus, which Bil'am wanted to represent.
As we find in Iyov (42:8), where Iyov was told to bring seven bulls and seven rams - R. Chavel's footnotes on Ramban. See also Ba'al ha'Turim.
Why did Bil'am not include lambs in his sacrifice?
Oznayim la'Torah: Because, based on the Midrash that "Par Echad" corresponds to Avraham, "Ayil Echad", to Yitzchak and "Kevesi Echad", to Ya'akov, 1 he was happy to bring bulls, which represented Avraham - since that incorporated Midyan 2 and Mo'av, 3 and rams, since they incorporated Edom; 4 However, he did not want to bring lambs, since they represented Ya'akov and re therefore confined exclusively to Yisrael - whom he hated and whom he was coming to curse..
