I've been involved with countless temporary PA rigs in all sorts of locations for TV - which often involves getting sound from a member of the audience, or a presenter moving among them while talking. And my rule of thumb is you can't have too many speakers as close as possible. It's also true that a good hand held mic beats a personal one on the lapel too - but as in TV you may have to think of the look of the thing.
And the snag is some members of the committee dealing with this prefer the look of a roof mounted array to wall speakers. My personal view is decent wall mounted speakers are the way to go. The walls of the church are plain plaster apart from the stone surrounds to the windows, so I suppose any speaker will be rather obvious.
I've already been down the route of using a different mic setup with the minister with my brother, and it's not on.