All Christians alike are priests. The authority of elders is no violation of Lk. Authority resides in the eldership collectively , not in any one elder independently. No, the local congregation is the divinely revealed functional unit through which Christians are to do the Lord's work, and elders are the divinely revealed overseers of it. The source and nature of the authority of the eldership.
Elders are such by the appointment of others.
The eldership is more than an executive committee to do the congregation's bidding. The evangelist does not confer authority here any more than he confers authority on the husband in a marriage ceremony. The authority of the eldership cannot be disregarded without disobedience to Christ. Obviously, elders have no revelatory authority in matters of faith - Jas. Elders are constrained by the Scriptures.