Hi Heartwood,
I don’t know all the answers but here’s something about the priests and saints as intercessors. It is mentioned first in the story of Abraham in Genesis, that Melchizedek was a priest. Later on the priesthood goes through the whole Old Testament, they offered prayers and sacrifices for the people, there are many references to this in the OT. One thing seems certain, priesthood existed in the OT, and God the Father in the OT, as well as Jesus Christ during his earthly ministry treated it as a legitimate institution. The New Testament priesthood seems to me as an extension of the OT priesthood. I don’t know why God wanted it, but it seems to me that it is in accord with His will for us to have priests. And as the OT priests offered animal sacrifices and holocausts (burnt offerings) to God, the NT priests offer instead the Eucharist as the sacrifice, wherein the Body and Blood, Soul and Divinity of Christ are truly present under the visible appearance of bread and wine. One thing is for sure, we non-priests (lay people) cannot offer the Eucharist as sacrifice to God, because we cannot consecrate (=change into the Eucharist) the bread and wine.
Another interesting story in the OT is that of Moses and the people, in Genesis. The people were so frightened by God’s presence and the majestic signs (pillar of fire, sounding of trumpets etc) of his presence, that they asked Moses to go up alone on the mountain and talk to God alone, in other words to intercede alone for the whole nation of Israel.
Yet another interesting story is that of Job, where God tells Job to pray for his friends, i.e. to intercede in prayer for his friends. See post #12 in this thread:
forums.catholic-questions.org/showthread.php?t=391651