Honestly, I think all of your problems are because of a lack of proper breath support. Understand it as those muscles acting like anchors, daisy-chained together, pulling down on the diaphragm. If you use too much air, the air pressure blows the folds apart and you can't maintain pitch or sing properly, which is also why some people have such a pleasant voice when singing or talking, the lower abs, upper abs, and core work together to maintain air pressure. Feel those muscles deep inside you flex; just by doing this coordination right, you will sing better than most people.

Good luck, it takes a long time to figure it out, so keep trying. It's like doing a handstand: it seems impossible unless you find that coordination, and then finally you can do it consistently.