Oh, oh, oh, oh, Trail is one of my favorite classes to compete in.
Okay, here goes nothing.
For the box, you don't pivot. It is usually 6' x 6', so it is way too small to do that. To teach the horse to turn around in it, I like to go corner to corner. So you go in straight, then to make a turn to the right, take the horse's front end to the first corner to the right, walking forward until you are as close to it as you can get. Then take the hindend to the left until it is about 1/2 way down the middle of the opposite side. Then take the forend to the next corner, move the hind end, repeat. Always stop at the corners, as when you get better at it, the horse will learn that if you stop with the front end perpendicular to a poll, they are supossed to exit.
For trail, also work on back throughs. You can use 4 polls laid out in different patterns, or you can use multiple cones. Start big, then get smaller.
Work on walk, trot, and canter over polls, concentrating on a straight line. Start with one poll, and as you get to where you can go straight and cleanly over one, put in another. The distance is about 24" between at the walk, 3'-4' at the trot, and 6'-7' at the lope.
Learn to work a gate (rope and metal), and take your horse over a bridge.
Side passing is essential for trail, both for sidepass obstacles, and to get into and out of other obstacles smoothly.
Unfortunately I don't have any trail patterns that I can attach here. I have lots in my head, but not on paper.
Other classes to try would be horsemanship and pleasure. For english, they should have hunter under saddle and equitation on the flat.
I have no idea about show clothes cheap. Those are awful hard to find.
Let me know if you have any other questions.