What is the significance of the triple blessing
Ramban #2: It refers to the judges who perform Mishpat, inasmuch as "Va'ahevcha" - Hashem will cause the families whom they have found guilty to love them; "u'Veirach'cha" - no harm will befall the judges following their harsh judgment: "ve'Hirbecha"
See also Ba'al ha'Turim.
What is the translation of "Sh'gar Alafecha"?
Rashi: 'The babies of your cattle'
See Peirush Yonasan.
What are "Asht'ros Tzonecha"?
Rashi #2 (citing Targum Onkelos) and Targum Yonasan: 'Your flocks of sheep'.
Rashi #3 (28:4, from Chulin 64b): They are called "Ashtaros" because they make their owners rich ('Ma'ashiros Ba'aleihen) and strengthen them