Yes 4-5 inch would work for corners and the straight lines. 10 feet is for both t posts and wood posts.
Basically an H brace is a twisted wire that goes from the top of the post to the bottom of the post. If a horse was running around or pawing there or kicked out, his leg could get stuck between the brace and the fence or get twisted up in the wire. I don't get any frost or snow here which is why we sunk the posts 2 feet into the ground. Good luck!
The mesh is attached to the post by a special staple (driven in with a hammer for wood posts, and they have metal clips for t-posts. You will also need a fence stretcher to insure the no climb is tight- SpeeCo Wire Stretcher - Mills Fleet Farm
You want to get the no climb as close to the ground as possible to avoid a horse getting a leg stuck- no set answer, but get it as close as you can.