1&2 - don't interact with fans. Ever. Regardless of level. If it's not a tourney, go to the head coach on that side and ask him to take care of it. If he won't they are his responsibility. Actions accordingly follow. If it is a tourney, get the site manager or director. If they are not to be found (often an issue), get a coach to call them. Lodge the complaint with them. It is their job. I get the usual arguments of they want to keep the coaches happy because the teams paid to be there, but this is an efficient way to handle it.
I ejected one fan ten years ago. It was a something that, let's just say was egregious and I needed to deal with. Ten minutes later the game ended and he was on the ground in handcuffs with four cops by him because he left the area, was intoxicated, and someone called the police. He then tried to fight them in the parking lot. I called my assignor and they told me "You're right, fans are not your problem but in this case had to do what you had to do." Local baseball director even called the assignor and complimented my handling of it.
As for #3, I've heard that happen with partners before. Don't like it, don't do it myself. As the umpire instructors at pro school would do, they'd tap your mask with a ball over and over until you got it in your head to trust your equipment. Yes, it stings/hurts/sucks, but this is our job.
Finally, nothing - NOTHING - irritates me more than failure to retrieve foul balls. I tell the coaches at the pre-game: "I need you and your teams help - everyone really - to bring back foul balls. Let's work together to keep the game moving and have your guys take care of your side of homeplate. I'll let you know when I'm running so if you could do me a favor and have a player run them out to me." Not perfect, but better than not addressing it. The "I'm too good to leave this bench and get foul balls" is something my old coach would have kicked our butts for. Did a tournament recently where if you brought a ball back to the tournament guy you got a mini-candy bar. I had eight baseballs at one point because the fans were on it.