Putting Harper at 1B would make him happier than a pig in crap. He'd be involved in virtually every play.
Even with some projection, Soto would be pretty clearly the worst defensive OF of all those guys unless Royce runs into walls at a rate of 1 a week. He'd have both the worst range and the worst arm (by quite a lot in the latter case). I think he can play OF, but I don't think he'd be anything but average in LF or below-average in RF. If the concern is to prevent Harper from running into walls, fine, but putting him at 1B wastes his best defensive tool.
