Two questions; two answers!
"Must a church have a plurality of Elders?"
A large and resounding "No!"
Biblically, otherwise there would have been no need for Paul to have left Titus in Crete to appoint the bishops/elders in the church or churches there. Nor would there have been a reason to return after some time to appoint elders in already existing churches, such as those in Lystra, Iconium, and Antioch. Nor did the church at Jerusalem start with elders, even after becoming not only the first church body, but a "mega-church" at that, for today's wannabe imitators, but they only had elders some years after the church was 'born'. (Ac. 11:30; 14:21-23; Tit. 1:5-11)
The real question should be:
"Should a church have a plurality of elders?"
An even larger and more resounding "YES!"
The very fact that Titus was left in Crete, in order to do this, and they returned to Lystra, Iconiom, and Antioch to accomplish this, shows its very importance.
In addition, I can find no instance, where any NT church had a single elder, as opposed to a plurality. The Jerusalem church had gathered a plurality of elders, even while having those with the gift of Apostle, in their midst. (Ac. 11:30) The 'church council' at Jerusalem had elders right alongside the Apostles, who appear to have equal authority, with even those who had been chosen by the Jesus (Ac. 15:6, 22,23; 16:4). The aforementioned churches all had this plurality of elders, as did the Church at Ephesus (Ac. 20:17), the church at Phillipi (Phl'p 1:1), the church James addresses regarding her sick (Jas, 5:14), and the church Peter is addressing (I Pet. 5:1,5) There was a plurality of elders who laid hands on Timothy (I Tim. 4:14), who BTW is an Apostle, confirming his gift, just as there were multiple hands laid on Barnabas and Saul by the church at Antioch, although here, these 'confirmers' are not identified as elders (Ac. 13:3).
{Pastor/Teacher is a spiritual gift, by express declaration. Why do we somehow think we can improve on the Bible, in this, by making Pastor and even worse, "Senior Pastor" the pinnacle of the offices in the local church??)
When addressing and exhorting elders of the particular church he is writing to in I Peter, he Peter does not initially here invoke his apostleship, but rather exhorts them as a 'co-presbyter', not that of any sort of primacy. Incidentally, for the two best known apostles, the 'Church' office, as relates to a given body, that Peter identified himself with was "sumpresbuteros" an elder of equal stature to any other, and Paul didn't even do that, but actually called himself a deacon, literally. Kinda' short on them 'control types', hunh?
The only times elder or bishop (singular) is used in an individual sense, that I find, is for identification, and qualifications, and culminates with the declaration of Jesus as Bishop of your souls. :jesus:
Multiple eldership important? You bet! That is exactly the reason why that this is is the practice and the model given in Scripture, IMO. :thumbs:
Ed