Q: Immersion in a mikveh / reading the Midrash
Q: 1. What is "Rav"? Does it mean Rabbi? A: Yes
2. Is a Noahide allowed to immerse himself in a mikveh (a ritual bath)? A: Yes, as long as he does it with the intention of purifying himself but not with the intention of becoming a Jew.
3. If the answer is yes, what are suitable words or a prayer for a Noahide to recite when immersing in a mikveh? A: "vezarakti aleichem mayim tehorim utehartem mikol tum'oteichem umikol gilulechem ataher etchem" ("I will sprinkle pure water upon you and you will be purified. I will purify you from all your uncleaness and from all your fetishes") (Ezekiel 36:25).
4. Are we allowed to read the Book of Midrashim? This is the only book we have, we don't even have a Tanach yet. A: You can read it. You should be aware that it is a book of oral law and it does not state historical facts.