James,
I've been involved with multiple churches dealing with acoustical issues. It's super hard (or I should say, impossible!) to find answers that satisfy everyone.
I'd like to relay my experience with my current church. It is in a newly repurposed building bought in about 2010, originally build as a grocery store and used for other purposes since. The interior design of the church space is wider than deep, and as the walls took shape I was extremely concerned about the acoustics. It's more than just internal volume (size) of the space and reverb time, it's also related to where the reflective surfaces are and their angles.
As the piano technician and as one of the primary sound system operators (at that time - not any more), and with previous church acoustical tuning experience, I asked if I could join the monthly project management meetings, and since I knew some of the members and they knew me they allowed me to join in.
It was a time commitment on my part, and required me to discuss the issues carefully so as not to offend the architect (who wanted it super 'live' because of the budget and materials being used) and those who were donating a lot of the labor force.
At one meeting after the room had taken shape, they had still not agreed with installing any sound absorption surfaces at all, so we walked over into the space and I demonstrated to them what slap echo sounds like - it was brutally strong when standing on the stage area. The reverb time in the room wasn't all that long, but the character of the sound reflections was loud and bright. They wanted a 'live' stage also, with hard surfaces everywhere (it was plywood at this time, so I showed them how loud and reverberant any walking was) plus talked about the noise transmission that comes between band instruments through the floor and can cause feedback. In addition, the air conditioners on the roof were not mounted on isolators, and they were running and rumbling that night (thankfully!) and the group was alarmed at how loud that was. I told them that our church would look beautiful inside, I complemented the design in general, but that the services would be very loud, it would be hard to understand the spoken word, and with strong rumbling from the 4 A/C units treating the roof like a giant bass resonator.
I prefer the sound of acoustic instruments in a naturally reverberant environment (like a good concert hall), but our church is primarily one with amplified sound, and I wanted to dampen the room down and allow the sound operators to control the sound, not have to deal with the room problems. They eventually came up with a compromise, with carpeting and stiffening of the stage floor (thicker plywood, stronger support) sound absorbing material on the back walls and some on the side. I was told that installing isolation dampers on the A/C units cost close to a million dollars! But wow, they really worked. Reverb and slap echo were well controlled, but the stage acoustics ended up being a little too loud still - the hard wood reflective surfaces on entire stage wall really intensified everything, and we couldn't control the band sound - the volume was being set by the drums and the stage monitors. However, the spoken word was very clear and comfortable for the person speaking, and we had good gain before feedback.
After some years we were able to make some changes to the stage by adding diffracting surfaces on the stage walls (for a while we hung decorative fabric there, later angled wood slats), plus more absorbing surfaces in the back of the house when the space was enlarged a bit.
If you're interested, services are streamed online and you can get a good look at the resulting room layout:
https://online.cclb.org/ This is probably not the same church shape that you have, James, and the music is likely different (no choir and organ in ours), so in that case the acoustical design should not be dampened as well as ours. But the process needs to be done carefully and with consideration of the budget limitations and general preferences of the church.
Good luck!
Don Mannino RPT