All great questions!
You are wise to wonder about the environment, as it matters a great deal in terms of resources, crowding, vibe, attitude of the staff, logistics, stress, and can greatly impact how you feel on test day and while taking the GMAT.
The first time I took the GMAT I took it in a crowded, very distracting testing center in the heart of NYC. I took it on a computer, in a room full of other test takers each at their own computer in an office. My anxiety level was off the charts and very differently compared to how I knew I could perform and had been performing on practice exams. There were people constantly coming in and out, the staff was unaccommodating, and I was given a small white board with a marker that would barely write and a broken eraser. I 100% should have scoped out the testing center beforehand.
This completely threw me. I waited a month until my next attempt, of course my confidence had taken a hit... but I never did another practice question or review during that month. All I did was work on calming myself, and finding the perfect testing facility. I believe I drove 90 minutes to 2 hours away from nyc, to find a small suburban town to a testing center that was low stress, quiet, had kind staff who cared. The result? My score shot up to where I had been performing on my practice exams.
I have now suggested this strategy for other standardized test takers of all types, and it has a significant positive impact on their scores from what I’ve seen. Low stress, visit beforehand, know what to expect, low anxiety.
So I didn’t really answer 1,2 and 3 in order, I’m just giving you my perspective on how much a testing environment can affect a person and how crucial it is to find the right facility. I personally think suburban and low traffic is the way to go.