Yeah, and Vic Damone has been playing at condo clubhouses ever since.

I agree that Johnny does indeed hesitate when Michael gives him the contracts, but after the hesitation, Michael pushes him even more by suggesting to him that maybe he could also persuade his Hollywood friends to join hem. At that point Johnny looks at the contract and smiles, saying he will do anything for his Godfather. I think he smiles because he sees the enormous amounts of money he will be getting for his appearances, and he realized that he can have all kinds of street creds with his Hollywood friends by getting them great money making gigs in Vegas, with all the Booze and Broads they can possibly dream of. And thus was born the Rat Pack.