Many shopping malls now have a CPR kit onsite. Walmarts seem to get more shootings than other stores, maybe every Walmart could have a trauma kit onsite. But certainly if you're organizing a security team for your church a trauma kit and appropriate training should be part of the plan.
I also once saw a video where the presenter had the minimum basics in a pouch about 4" x 4", the type with a velcro strap to attach to the same belt you carry your gun on.
Maybe. People sometimes focus too much on the kit and not enough on the skill. The old boy scout teaching of holding direct pressure is really one of the best options out there. CPR is of limited utility if a patient has cardiac arrest after penetrating trauma. If there isn't any blood in them, chest compressions don't do much.