1)
Is this the same angel mentioned above?
1.
Malbim (here and in Shmuel II, 24:18): Yes. Since he did not do his mission (for Hashem told him to refrain), he gave the Nevu'ah to Gad; prophecy comes via angels. The destroyer himself prepared the cure for them ? "Machatzti va'Ani Erpa" (Devarim 32:39), "Yimchatz v'Yadav Tirpenah" (Iyov 5:18). Also the miracle of fire descending [from Shamayim] to the Mizbe'ach (verse 26) was via the angel.
2)
Why did he say "Ya'aleh"?
1.
Radak (Shmuel II, 24:18): Aravnah's granary, the place of the Beis ha'Mikdash, is higher than Yerushalayim.
