I'm just popping in to say that, although not chargen-legal, the Auto-Assault 16 is in fact superior to all other shotgun options. Yes, it's a bit pricey, it doesn't come with its own smartgun system and it's not the most accurate shotgun. But, it has the highest shotgun damage, full-auto capability, a respectably large ammo drum and (this is the really important bit) 2 points of built-in recoil compensation that aren't attached to any accessories. Slap gas vent 3 and a shockpad onto the AA-16 and you've got yourself 6 recoil compensation. I'd do even though I don't even need that much, just so that the decker or someone else could use it if I went down.
If I were you, OP, I'd take the Krime Boss as your default shotgun and add some mods to it but instead of buying the Mossberg as your serious business shotgun save your chargen money and purchase the AA-16 with accessories after your first run.