Custom Horse Tails, Equine show horse tail enhancers, custom horsehair tails, horse hair Custom Tails
^That website makes really nice customs for a good price. They also make the tails made for horses with no tail hair to attach a regular tail extention to. I don't fully understand it, but it attaches onto the hairs and tailbone somehow. They're called rendered tail I think.
4-H level, don't worry about a tail, but anything bigger, a fake tail would probably be good.
What Farmpony said. They have to know how to give to the bit, and relax into the bridle. It will take some time, but short and sweet sessions. It's best to start from the ground, and work up into the saddle for headset.