As to the mags, only use MecGar mags! That is who makes the mags for Beretta. But you can usually find them a little cheaper separately than buying them through Beretta. They are very high quality and do not have the drop free and jamming issues the cheaper government contract mags have.
ALSO.....
You can now make ANY 92F gun or newer into a decocker only model for just $55 using the Beretta conversion kit.
Beretta M9 - 92/96 G Conversion Kit
It seems that Beretta USA is out right now. But I have been able to find them on other websites too.
This helps a ton and now I like my 92F (not FS) more than ever before. The kit I got was very well built and seems to be durable as well. It is all metal with no plastic parts and even extra springs and plungers in case you loose one.
Well...well worth the $55 IMHO!
I'm hoping there will be some milsurp m9's some day. I'd love to have one. I'd be sorely tempted to get one and do exactly as you describe.