I'm way too tired to read through all the post, but this is my experience:
My current horse, Kainne, was the first horse I went to see. I had looked at a ton online, asked a ton of questions to people online, talked with my trainer about horses online, but Kainne was the first one that I went to see in person.
I saw his ad on BAEN, a few days later went to see him with my trainer (she is a very reputable dressage trainer in my area), rode him around a bit, and we both fell in love with him. She said she'd be more than happy to see him brought home straight away, and so the next day he was stalled in my home stable.
I wouldn't regret it for a second. He's a wonderful, lovable, very willing horse.
So I say usually it is best to look at as many horses as possible, but there are exceptions. Hopefully you've had a professional see the horse to confirm that he is a good match.