Dilly, I agree that he's a very attractive horse and I can see why you're drawn to him, but I still suggest that you start with some lessons on a horse that is maybe a little more people friendly. I have no idea what your financial situation is like, but if you're able to afford it, you might look around for instructors in your area, especially since your SO doesn't seem interested in teaching you the proper way to handle a horse safely. While I'm sure you love him and he loves you, his suggestion of "You wanna mess with him? Tie him up and mess with him" is a good way to get a novice horse-handler hurt. With an instructor on a good lesson horse, you can learn the correct way to avoid injury and handle any one of a million unforeseen reactions that might happen.
THEN, when you've got a good start and can confidently handle a horse on your own and handle most normal horse reactions, then you can get your guy evaluated by a trainer just to see where his training level is at. It is easy for us to make assumptions about horses just based on a few written sentences on the internet, but often those assumptions are all wrong. This horse may be completely unsafe for someone of your ability to handle or he may be the perfect gentleman who will be a great first horse for you to learn to handle and ride, but you won't be able to figure that out on your own and we can't figure it out on here. Your best bet is a hands on evaluation by a trainer. They can tell you what his initial training was like and whether there are any gaps in training that need corrected before you work with him.
In spite of what Walkinthewalk said, not all Amish are "notorious" for mishandling their buggy horses, I am good friends with a lot of people in a good sized Amish community up in Kansas and they all treat their animals well regardless of whether they are a buggy or plow horse. No offense, Walkin, but generalized statements about how the Amish are these horrible abusive cruel people to their horses just tick me off. IME, there are good horsemen and bad horsemen, no different than anywhere else in the world, they just seem more prominent because they all have horses, not just a few of them like us "English". They seem to catch the brunt of the accusations because of "assumed" abuse and because they aren't around the net to defend themselves. Just because they use their horses as equipment instead of pets doesn't mean that they are abused. Lack of pampering and "loving" doesn't mean abuse either. IMHO, that's why most people who see Amish horses that are stand-offish automatically assume that they've been mistreated...because people are so used to those horses who follow people around and have their nose in your business all the time, anything less means that they haven't been treated "kindly".
ANYWAY LOL, sorry for the rant, but I have many Amish friends and I know how they treat their animals and it just bothers me to see them clumped together in a stereotype, especially when they don't have internet and can't defend themselves.
Dilly, the reason that I strongly suggest you get help from a trainer is because figuring it out for yourself is dangerous. Even learning from a very experienced horseman, I still learned a lot of lessons on my own...usually on the other side of a nasty fall, broken bone, concussion, or some other not-so-minor injury. I can't imagine trying to learn everything on my own. I probably never would have lived long enough to reach puberty LOL.