I will completely agree with you that I am not qualified to Design a sound system on my own. I am also part of a military community in Italy and at the moment of construction being started as soon as our Lock Down is lifted. So I am the best hope they have at getting proper wiring run before it is too late. I would love to have more time but unfortunately I can't just go to the closest design firm and hire them. My experience is in Home theater Installations and running sound at churches for 15 years. I have never designed a commercial or Live music venue before. I know just enough to help but not enough to go at it alone which is why I am asking questions.
Do you have any experience with the VXL Line Array speakers that I asked about possibly using for a Live Music event?
Mike answered your question, the fact that you did not consider the pattern of the loudspeaker takes us down that same path. While the logistic situation may be unique certainly the space is not unique, reverberant reflective rooms are very common.
If you want meaningful help:
1 - Attach a drawing of room including the ceiling height at multiple locations. Note what each wall is, glass, concrete etc.
2 - Are your dimensions in feet or meters?
3 - What you described situation wise, is it really an advantage to install permanently
4 - What is your total budget for loudspeakers and amplifiers?
You don't have the time and resources to do it right. Are the people spending the money going to be OK with an unusable, unintelligible sound system? My guess is because you are the sound guy that have complete faith in your ability to execute. I suggest you have a face to face with them.
Designer does not have to be onsite. They can work with your remotely.
Stop fixating on brands and models and do a design first, it's like picking out a jet engine before you know the fuselage and wing design.