9mm SAAMI specs are a maximum chamber pressure of 35,000 PSI.
.357 magnum is also 35,000 PSI.
Problem #2: I could be wrong on this one, some shooters more experienced with moon clips might help, but unless your cylinder has been designed to use moon clips, the clip and the rear of the cartridge would again take up too much room, and you would not be able to close your cylinder. BUT, since the 9mm cartridge will not fit anyway (Problem #1), it's a moot point.