Safety is first, comfort is second. If height bothers you, dont go that high. A nice seat will go a long ways in staying still, alert and able at crunch time. Make sure you have a good back drop and good cover to prevent skylighting your outline.
Always check the tree you want to set up in. In the fall, sometimes leaves arent there...make sure the wood is solid, and it isnt near any widowmakers.
Spend the little extra cash it takes and get a rope to attach to at ground level. Climb safely.
And always try to make sure atleast two people know where you are, when you will be back, and how to find that spot if needed.