1)  I noticed he had the option to be told to use a stealth boy, so I gave him three.  In our next encounter, w/o prompting, he used all three of them!  In one shot!  heheh.  
Yes, he'll go right through the Stealth Boys!  I only give him one at a time through the dialogue. 
2)  I was leaving the Statesmen Hotel after doing Reiley's Rangers.  Brick had died in the exodus and I looted Eugene.  Overweight, I stashed Eugene in an ammo box outside the hotel, figuring I'd come back for it.  Mutants immediately jump us in the streets outside and the next thing I hear is the whine of a mini gun and there's Charon charging them using Eugene!
Good for him.  So I guess he didn't go berserk on you with the Rangers then?   
3)  As much as a hazard it was, I always liked it when Charon would chuck grenades too.  He has about 20 frag grenades in inventory, but I haven't seen him throw any...
It's nothing I've done to him.  He's often done that with me in vanilla playthroughs.  He really doesn't use them all that often.  He threw a few today when I was playing.  Of course, they hit me  :shakehead:  and I think his target was a bloatfly or two.  He never uses them when I want him to. 
He started singing or humming today and made me laugh  :whistling:
I have to say, of all the Idle pvssyr I added, the humming is my absolute favorite.