1. The Maharsha explains that Michael, the angel of mercy (represented by water) does his task quickly in one flight. Gavriel, the angel of Din (represened by fire), needs two flights in order to give a person time to repent and alter the Din. Since Eliyahu is comprised of the four elements, not only water and fire but also air and earth, he is not capable of flight without 3 stops, or 4 flights, and the Mal'ach ha'Maves takes 8 flights so that one has time to repent. I was not able to find other explanations.

2. Elazar bar Avina is listed in Seder ha'Doros (Amora'im, Aleph) and is also mentioned, in Atlas Etz Chaim by Rav Halperin, as a third generation Amora from Eretz Yisrael.

All the best,

Reuven Weiner