This entry is in answer to: “So did Mr. Knightley go to church with Emma? And what about the wedding? Was there some sort of “custom” for who got married in whose parish, i.e., the husband’s came first, etc.?“

Mr Knightley probably did not attend the parish church in Highbury. He lived in a separate parish, Donwell, and in all probability that parish had a parish church or chapel where he could attend.

I say in all probability for in some parishes in the Church of England there was not a suitable place of worship. These places were called “extraparochial places.” We have no idea if the Donwell parish was one of these. However, I think it highly unlikely because of the ecclesiastical nature of the Donwell estate (it was once a functioning abbey and adjoining estate- like Stoneleigh Abbey: a place with strong family connections which JA visited in 1806 and which influenced her writings.

Mr Knightley and Emma were most probably married by Common License issued by a bishop, as were most genteel people who didn’t qualify for a Special License. Only those who could not afford a Common License were married by the Reading of Banns in both parishes (as it would have happened in this case). It was thought to be degrading to the bride-to-be that everyone in the parish knew that her wedding night was fast approaching when the banns were read, so to save your brides blushes if you could afford to, you obtained a Common License by applying to your Bishop. The qualification for obtaining a Common License was that, of the couple to be married, one or both of them had to have been living in that parish in the Bishop’s diocese for a qualifying period of four weeks immediately prior to the granting of the license:

And it is hereby further enacted That no License of Marriage shall, from and after the said twenty-fifth day of March in the Year one thousand seven hundred and fifty-four, be granted by any Archbishop, Bishop or other Ordinary or Person having Authority to grant such licenses, to solemnize any Marriage on any other church or chapel, than in the Parish Church or Publik Chapel of or belonging to the Parish or Chapelry, within which the usual Place of Abode of one of the Persons to be married shall have been for the Space of four weeks immediately before the granting of such License….

See: The Clandestine Marriages Act (1753), Section IV.

So in theory either parish could have been the place where the wedding took place. However, I think the text indicates that Highbury would have been the parish where the wedding was conducted, as Emma herself envisaged:

Before the end of September, Emma attended Harriet to church, and saw her hand bestowed on Robert Martin with so complete a satisfaction, as no remembrances, even connected with Mr. Elton as he stood before them, could impair. Perhaps, indeed, at that time she scarcely saw Mr. Elton, but as the clergyman whose blessing at the altar might next fall on herself. 

and

The result of this distress was, that, with a much more voluntary, cheerful consent than his daughter had ever presumed to hope for at the moment, she was able to fix her wedding-day; and Mr. Elton was called on, within a month from the marriage of Mr. and Mrs. Robert Martin, to join the hands of Mr. Knightley and Miss Woodhouse. 
Chapter 55

It would also be the main choice of venue in deference to Mr Woodhouse’s feelings and health. Remember the manoeuvres needed to get him to agree to visit Donwell Abbey for the strawberry picking party?