It seems quite unfair to me that your wife has decided exactly how she wants her polyfamily to be constructed without actually consulting you or taking your desires into consideration. She's allowed to move some guy in and you don't have veto power, and you're also not allowed to casually date? I don't think you guys should have to subscribe to the exact same version of polyamory. I mean, sure, in a perfect world you'd want the same things, but you're both individuals! She should be more willing to compromise... After all, she's asking quite a lot of you, and awfully fast!
I am the kind of person who falls in love easily, and who moves in quickly, and I still feel like this is a bit sudden. You might have him come stay with you guys (or at a hotel) for a weekend so you all can meet up before you have him just move in. Your wife might decide after spending a fully 48-72 hours with him that he has obnoxious habits, or there's no real chemistry... I've done the long distance-to-in person thing before, and just talking is different that spending time with someone. I was completely head over heels for some guy I met online a few year back, and it felt like the feeling was mutual. After about a month of living together, though, his feelings began to fade and I was crushed. Your wife might even experience something similar. You guys are all pretty young (I'm not trying to sound cocky -- I'm 24 myself) and feelings that seem like they'll last forever can sometimes change easily. Especially this younger outsider... You were a 19 year old man once yourself... I'm sure you know what I'm getting at
I'd say you guys should at the very least talk a LOT more about what you BOTH want before you rush into anything.