I can only answer one part of this question. You can have whatever you like at a church ceremony. We were married in church, because we thought it was more permanent (it was - we have been married for 61 years) and as we could ony afford the minimum, we had no hymns and no other trimmings, only the actual wedding ceremony. Hope you get the answers to the other parts of your question.
If you want to be married in church, why don't you ring your local priest straightaway and have a word with him? You don't have to have a ceremony with all the trimmings. It can be as simple as you want it to be.
We got married by a Minister in a hotel, the Wedding vows were traditional and a short prayer was said but we had had non - religious readings and songs by family and friends.
I think the ' rules' may be different up here in Scotland or perhaps have changed in the ten years since our wedding.
Where abouts are you based? I'm just back from a ceremony in a hotel which was performed by a minister and we had a hymn! Not sure whether it was a civil ceremony or not (although i think not!)