1)A vicar means a representative and all those in holy orders are "pastors" in the sense that the term "pastor" is rooted in "pasture"---in other words, one who shepherds. Scripture is more explicit with
bishops, priests, and deacons. Perhaps this helps.
Bishops (episcopoi) have the care of multiple congregations and appoint, ordain, and discipline priests and deacons. They sometimes appear to be called "evangelists" in the New Testament. Examples of first-century bishops include Timothy and Titus (1 Tim. 5:1922; 2 Tim. 4:5; Titus 1:5).
Priests (presbuteroi) are also known as "presbyters" or "elders." In fact, the English term "priest" is simply a contraction of the Greek word presbuteros. They have the responsibility of teaching, governing, and providing the sacraments in a given congregation (1 Tim. 5:17; Jas. 5:1415).
Deacons (diakonoi) are the assistants of the bishops and are responsible for teaching and administering certain Church tasks, such as the distribution of food (Acts 6:16).
2)Acts 15 is an example of a group of the elders gathering under the guidance of the Holy Spirit.
3) Bishops do not bear entirely every charism of the apostles. For instance, they cannot add to the deposit of faith taught by the Apostles, which is the foundation, although they can build upon the foundation. The historical record of the early Church's understanding clearly details that the bishops did indeed succeed the Apostles (e.g. Irenaeus,
Against Heresies, 3.3.3-4, ca 170 A.D.) Another way to recognize the lineage of succession is to recognize the priestly ministry in the Old Covenant. For instance, the tribe of Levi (the Levitical priesthood) bore succession through genealogical descent. In the New Covenant, the priestly ministry bears succession through the more superior spiritual descent.