>> I submit major metropolis was a city. The rest were not. <<
That’s not reasonable, given the context. Paul and the apostles themselves did a pretty thorogh job of establishing churches in each major metropolis, and would have appointed presbyters themselves. The letter to Titus is Paul appointing a fairly minor character to do so. And such presbyters were needed sacramentally. We see from Acts 3 how deacons such as Phillip weren’t sufficient even to lay hands on converts. We can suppose that Paul is concerned that communities of believers are popping up where there is no presbyter to administer sacraments to them.
>> We have really no way of knowing how structured they were or even how “catholic” they were <<
No, as I concurred, there was probably massive variation among local traditions. But even so: the Thomian (I would have said Thomistic, but you’re trying not to refer to Acquinas? ;^D) churches give us a good hint.
How many "cities" were there and which ones? Biblical numerology is not always trustworthy. I mean, we have 600,000 male Hebrews and their families (more than one million people) allegedly roaming the Sinai desert for 40 yearsand (most of which were spent in one single place) and not leaving a single archeological piece of evidence of their presence!
We don't really know for sure how many followers were there of the early Church. The data are simply not reliable.
One could equally well argue that there were just not enough converts to leave around as presbyters of local communties, given the 5,000 mile spread you mentioned earlier.
I believe Rome would have felt a lot more threatened by such a vast organization that denied caesar's divnity then historical facts show. In fact, one of the problems with 1 Peter being authored by Saint Peter is that it addresses the believers in scattering (probably refers to the Jews who left Palestine 500 years earlier) as there were no Asia Minor persections of Christians in Peter's lifetime.
But even so: the Thomian (I would have said Thomistic, but you’re trying not to refer to Acquinas? ;^D) churches give us a good hint
My fault. I knew soemthing was wrong with that adjective but couldn't think of the correct one. Anyway, shouldn't it be Thomastic? :)