Regarding seudas Rosh Chodesh Av. I saw that the Chidah brings to eat meat even on Rosh Chodesh Av lichvod Rosh Chodesh. Do other Poskim confer with the opinion of the Chidah.
The custom of Sephardim is to eat meat on Rosh Chodesh. However, the Ashkenazi custom is to refrain from meat even on Rosh Chodesh.
See Mishnah Berurah 551:58; Kaf Hachaim 125.