Aquila, please do not take this as an argument. I am not arguing. I agree that there is a lot we don't know about the origins of Christianity.
As far as John baptizing in Jordan,
Matthew 3:5-6 says that people "were baptized of him IN Jordan, confessing their sins.
As far as the two Messiah thing, there was a belief among Jews that there could be two Messiahs. This was based on two different sets of prophecies concerning the coming Messiah. One was identified as Messiah ben Yosef, who would be the suffering Messiah and would be martyred. The other would be Messiah ben David, who would rule from David's throne. We see a hint that John may have believed that or may have considered it in
Matthew 11:1-3 when he sent disciples to ask Jesus if He was the One to come or if they should look for another.
As far as I know there is nothing in writing available to tie John the Baptist with the Essene community. From what I understand they were a separatist group who looked down on the established priesthood system in Jerusalem and who were looking for Messiah and His kingdom.
Luke 1:80 speaks of John being in the wilderness from some time in his early life until his shewing/manifestation unto Israel. We don't find anything in the Scriptures about his teaching or ministering in the Temple. Instead, he seems to be separate from it.
As far as I know we don't really know how the Jewish mikveh started nor do we really know where John got his idea to baptize people or why Jesus continued the practice. We ASSUME it was the mikveh and Gentile convert thing. Since John practiced it, then Jesus continued it, it just seems to have been carried over into the church as a Jewish practice.
Yes, I can see the symbolism of Jesus being washed/sprinkled by a priest to release Him into the priesthood. And, in
Matthew 21:23-27 when Jesus was questioned as to where He got His authority to minister He seems to tie it in with John's baptism.
Your speaking of sprinkling or pouring as water baptism may shake some people up here. We are just so used to insisting on immersion --even complete immersion to the point of rebaptizing someone if a body part is not completely covered the first time. That has become a Pentecostal tradition and insisted on by most Pentecostal groups. My reason for quoting the Didache/Limuda (which some consider only tradition and some consider Scripture) was just to show that possibly even in the days of the Apostles, three fold immersion or pouring were both in use and the traditional FS&HG formula (gasp, shudder) was referenced.
I'm not being contentious or trying to debate. I admit there is a lot we don't know for sure.