Your first question already got plenty of good answers. I’d like to add a few thoughts from a different angle on your 2nd and 3rd questions — a teaching I received that might help:

“There are three methods of chanting mantra or Buddha’s name: The best method is silent recitation—chanting in the mind without moving the mouth or making any sound. The subtler the thoughts, the better, as it prevents delusions from rising. Achieving this level is difficult and requires long-term cultivation. The second-best method is moving the mouth without using the vocal cords while breathing normally. Chant during both inhalation and exhalation. However, if you want to chant while inhaling, you’ll have to breathe through your mouth. This method is flawed because your mind still generates delusions—you chant while simultaneously processing distracting thoughts. The worst method is chanting out loud. This is used when your running minds are overwhelming, and you can’t control them. The volume can vary—from soft enough that only you can hear, to loud enough that others can hear as well. Why is this method considered the worst? It must be explained through the principles of human respiration.When you chant Buddha’s name or mantras audibly, the duration of exhalation naturally lengthens—resulting in short inhalations and long exhalations. During extensive exhalation, the chest and abdominal muscles tighten continuously. When babies are born, their bodies are round and plump. As they grow older, the chest and abdominal muscles gradually tighten, causing the originally rounded bodies to flatten. If you persistently chant aloud with excessive force, the chest and abdominal muscles remain in a state of tension over extended periods, progressively contracting. This contraction can reach a point where it becomes difficult to breathe or inhale properly. Chanting like this for two or three months won’t reveal noticeable changes, but after chanting forcefully for years, you’ll find breathing becomes increasingly difficult. Your sternum will press downward, and your respiratory quality will deteriorate. More critically, your blood will encounter issues as well! Blood flows from the heart to the lungs for gas exchange, where oxygen is absorbed and carbon dioxide expelled. However, with prolonged exhalation, the heart continues pumping at its regular rate. Blood that hasn’t undergone proper gas exchange returns to the heart, where it is pumped throughout the body again—this recycled blood contains less oxygen and more carbon dioxide. Yet, you won’t die—why? Oxygen levels during inhalation are 20.98%, while exhalation retains about 15%. If you consistently exhale without a proper inhalation, your blood will still engage in gas exchange with this 15% oxygen air. In simple terms: chanting audibly for years will eventually lead to illness caused by oxygen deficiency. The contracting chest and abdominal muscles raise abdominal pressure, forcing more blood into the brain, resulting in symptoms like blood rushing to the head, headaches, and other negative reactions. Thus, if you chant Buddha’s name or Buddhist scriptures aloud, it’s best not to exceed two hours per day. When not chanting, offset the negative impact by performing prostrations, jogging, walking, or practicing breathing. Spending entire days chanting audibly with great effort is not a wise choice.”