Should only Bnos Yisrael cry over Sha'ul?
Malbim #1: This excludes David. He himself did not cry over Sha'ul, for Sha'ul pursued him.
Malbim #2: They should cry due to the benefit that they received from him [like the rest of the verse explains].
Why does it say "ha'Malbishchem Shani Im Adanim"?
Rashi citing Targum Yonasan: He dresses you in colored clothing, and gives to you delicacies. Radak citing R. Yehudah, in Midrash Shmuel 25:1 - when their husbands went to war, he financed their wives. Since he gave also delicacies, we learn that ornaments are proper only for a body pampered with delicacies.
Radak citing Nechemyah, in Midrash Shmuel 25:1: "Bnos Yisrael" refers to Sanhedriyos - when Sha'ul heard a Chacham say a nice reason in Halachah, he would kiss him on the mouth.
Radak: "Adanim" can refer to nice garments. They are pleasure for the body just like good food.