You'll have to decide on which horse collar w/o my help. I know next to nothing about driving. You could join a horse driving group on the Internet and ask them. Are there reviews up with people's input about the plusses and minuses of each? That's often how I choose products when I'm unsure which to get.
Speaking of products, what kind of coffeemaker did Hubby get you? Do you like it?
I assume if you need to use the stud chain when leading Nevada that he's trying to go faster than you want him to. A good tactic is to walk along with him, and when he gets in front of where you want him, make him back up. I like to use a whip on the horse's chest for this. You don't have to beat the horse -- just tap, and if nothing happens, tap harder. If still nothing happens, then a smart swat. Make him back about 3 steps, then go forward again. In about 3 steps, he may get too fast again, so you repeat the process. Soon he learns to back from a gentle tap instead of having to be more forceful. And if you do this every time you lead him, backing him every single time he gets ahead of you, soon he stops doing that. The secret is to be totally consistent. Don't do it sometimes and not others. And expect your progress to the round pen to be painfully slow at first. You will be going backward as much as forward. When he responds better than before, put him back in his pen and feed him hay or some other goody like a carrot. Till he leads well, there's no point in trying to do anything else with him, just focus on that. Parelli said something like, you need to take as long as it takes. Taking the time to do it right actually takes less time than constantly fighting. I bet if you are totally consistent with the leading, he'll learn it in about a week if you do it every day for about 1/2 hour. Even if you don't do it every day, he can still learn. In fact, I found out something interesting when I was training Penny. Sometimes we'd work on something, and she wouldn't quite get it. I'd return to the barn after a day off, and she'd get it the first try! What did she do? Study the problem while she was grazing? Anyway, I've heard other horse people say they found this out, too, so sometimes, I think you make more progress with less work when you skip a day of training. Of course, it takes longer because you aren't working on it daily, but it actually takes less working hours. Horses have excellent memories, and once a horse gets an idea, it sticks with him -- for good and bad. Bad habits are hard to break for this reason.
Once you have the leading problem under control -- and he may look like he learned it but test you from time to time to be sure the rules are still the same -- just like a kid -- then you can move on to round pen work.
To get him to turn toward you, use a long lead line -- about 12 feet for a horse, but you can probably get away with one a little shorter for a mini. Use a whip that'll reach him from the end of the line. Make sure he's not afraid of the whip but respects it. You should be able to gently rub him all over with the whip without him getting nervous and moving away from it. The whip is a signal, not a threat.
Once he's used to the whip and knows to go forward when you wave it at him, have him circle you at the end of the lead. Ask him to slow or stop with a wiggling of the rope. Meanwhile, point the whip at the point of his hip -- where that bone protrudes. He should move his hindquarters away from the whip while you pull his head toward you, and that'll get him to turn toward you. Once he gets that idea, use the whip less and less. At first, you may have to tap or prod him with it to get him to turn his .... away. Then you may just point it at the hip and he'll turn away. Finally, you can just move, leaning a bit toward his ...., and he'll turn away. Then you can try it without the lead attached, once he does it w/o you pulling his head toward you and just from leaning toward his ..... Don't move your feet more than one step. The idea is for him to move his feet and you to stand in one spot while you make him move.
If you try this, tell me if it works. it worked with Penny, but I had an instructor hovering, telling me if my timing was off, and timing of signals is important. It's really better to have someone on the spot to watch you work with him and tell you when you made a mistake right then. At least that's how I learn.