I would consider acceptable proficiency for carry (and this is my standard and noone elses) to be able to get all hits on a sillhoette target at 25 yards slow fire, 4-5" group at 7 yards slow fire, and 12" group at 7 yards doing rapid fire/double taps.
What I would be more concerned about instead of shot placement though is safe weapons handling. Are you ALWAYS aware of your muzzle direction? Is your finger on the trigger ONLY when you're on target, and off the trigger while doing reloads, drawing and holstering, etc? These are far more important than shot placement.
Think about this: If you were shooting next to someone at the range, would you rather shoot next to a guy that was all over the paper at 7 yards but meticulous about keeping the barrel down range, and handling the weapon safely, or next to a guy that can shoot a ragged hole at 7 yards, but sweeps people as he shoots or has his finger on the trigger when loading, etc?
Safety first! Accuracy will come with practice.
As for your second question, yes failure drills are a very useful skill. I would not seek out shitty ammo to do this though, because ammo that repeatedly misfires shows poor quality control, to the point that you could have a double powder charge, or a squib (primer, no powder, bullet gets stuck in barrel, next round gun goes kaboom). Use dummy rounds. Have someone else load your mags to the order is a surprise.
This is also a good drill to see if you're flinching. Your barrel and sights should not move when you pull the trigger on an empty chamber and the gun goes click.
It sounds like you realize that carrying a loaded firearm in public is a big responsibility, and something that should be taken seriously. Check your local range to see if they have any training programs. You'd be amazed what a couple hours with a good instructor in a one-on-one situation or a few hours of supervised range time in a group will do for your skillset. It's worth every penny!