CoolBreeze2106
Concerning evidence for COA.
You need only supply evidence if either or both had ever been married or in civil partnership before. (eg Divorce papers in English language)
Other than that it's only a signed declaration by you both (on the form) that you have not been married (or civil partnership) ---- False declarations have dire consequences.

Regarding marriage in Anglican Church it can of course be done under most circumstances but only you and your fiancee know these. Best to discuss with your local
Church.
Sorry I am not knowledgeable enough on this area to give advice.