I apologize for me bluntness but....
I think this young man needs his own life. You definitely should not have him move in! Let him develop some life skills and relationship skills. He sounds like he is totally fascinated by the sexual side of things but really, what 19 year old guy isn't?
Your wife sounds like she is in the throes of New Relationship Energy which probably means she is thinking with her heart and vagina, not her head.
Seriously, we have seen people move into together who were much more experienced and they imploded because the fantasy is a fuck of a lot different than the reality.
If this is real they both should be able to pace themselves. I also get the feeling your wife may be entertaining the idea of you having other partners just to make it "more fair" for her to bring this guy into your bed. I wonder how she will respond if you hook up with a 19 year old girl and decide to fuck her in your marriage bed? Because that is the reality. She has got to be able to handle you doing the exact same things she will be doing with her young man.
Just the questions this guy is asking are raising huge flags!! They are so far ahead of themselves its unbelievable....Pace, pace, pace. He sounds immature and I think you will have serious regrets if you let this guy move in.
When your really in love you should be able to be patient...when your really horny it is sometimes more difficult...this guy sounds horny...does he have any real relationship experience?
Take care and slow down
Playing the Game of Life with Monopoly rules.
Monogamy might just be in my genes
Poly Events All Over