RE: how high?
The vast majority of hunters I talk to are guilty of two things:
1) Vast over exaggeration/little or no concept of what one foot of height really is. I have had more people than I care to discuss come through work talking about how they only hunt from 45 feet up in a tree. Most trees in my part of the world ain't that tall, and the ones that are ain't thick enough to hold a man that high. 25 feet can seem like a mile when you are up there.
2) Hunting WAY too high. 25 feet might as well be a mile. I had one stand last season that I hunt 27 feet to the platform. 25 yards was dang near straight down. I'll never get that high up again... no need to.
I hunt from between 15 and 20 feet (to the platform) depending on cover. There have been plenty of deer I have arrowed from 12 feet... just gotta have the cover for it. Any lower than that, I'd rather be on the ground.