How much to bell the case mouth?
Getting back to the original question, I load nothing but lead for pistol rounds, and when I started I was told that the merest hint at belling was enough; just so the bullet could be started into the case by the press, without the 3 of them having an argument about it.
Thousands of rounds later, I have yet to have a case neck work-harden enough to split, and the few bullets which have argued about going meekly into the mouth of the case have been operator error (setting bullet on case mouth at too much of a tilt; they like to be just about straight).
As to working the case mouth, you also want to crimp the bullet only just enough. With light target rounds, this translates to "almost not at all," but with heavy hunting loads you want a heavy crimp. Still, even my hunting cases haven't split due to excessive working of the case mouth brass.