Porter, Michael Cayley will respond to the question regarding the English monthly meeting.
For correct names of American monthly meetings, your best source is QuakerMeetings.com and I have pointed that link to the search form.
In American meeting records, what you will want to look for is a minute establishing their affiliation with a particular meeting (this can take the form of acceptance, transfer or even just a preponderance of family records). And, keep in mind that some records including marriages, births and deaths may be found in the records of more than one meeting as these were reported 'up the chain' to Quarterly and sometimes Yearly meetings and may be recorded in other monthly meetings where other parts of a family were members.
All of that said, you are looking in a place and time in Pennsylvania and environs where many records are not yet digitized or indexed. These records are usually held by Swarthmore/Haverford TriCollege Library. The meeting listing at QuakerMeetings will give you the location of the records but not all of the links have been updated.
Lastly, there are some errors in American monthly meeting locations caused by a 2019 bot deployment that made errant corrections. Quakers Project is correcting these as they are found so please let us know if you find something that doesn't seem right. The name of a Quaker meeting does not always mean that was/is the location of the meeting (the bot seemed to think it did).
Edit: apologies but I forgot one of your questions. There is no size requirement for a monthly meeting. If the meeting is documented it is appropriate that it have a category created if there is a profile to place in it. One benefit of QuakerMeetings.com records is it will tell you any predecessor and successor meeting names.