Thanks walkinthewalk, I think you summed it up perfectly.
I might actually do some testing for Cushings and IR in this horse because he is so fat. Just to be safe. It does sound legit, but I'm waiting for the flaws to show up. Because otherwise, except for the excess weight (which can be lost, though it might mean he has to be dry-lotted, and so not in the same pasture as Harley, but they could get to know each other over the fence), he sounds too good to be true.
Harley would not be able to see his old pasture mates at our place. We live in the country, so when I say neighbor, that doesn't mean we can actually see each other :) They would hear each other calling, but we've brought him here a few times to be ridden and hand-grazed a bit, and he's never called out to them. So I actually think he might be ok. In fact, I think it might be nice for him to have the place to himself at first. He's always getting bullied and pushed around by other horses, so this way, he'd be able to relax for a bit and "claim" the property for himself before the arrival of his friend. I would also consider putting this "fat" horse in a training refresher to help him get fit before he gets here. But if he's good on trails, I'd take him out everyday for a solid hour or two and work him. Maybe eventually pony Harley along just to desensitize him.
I don't think I would actually resort to getting a mini. Because then when we found a second horse, we'd still be stuck with the mini taking up space.