Teeth whitening concerns & questions

I am someone considering teeth whitening. I’ve been looking at YouTube, Naver, and various other sources, and I have some questions. I want to hear opinions from different people, so I am posting this message.

1. How much does it usually cost? Is it priced per tooth?

2. I heard that hydrogen peroxide is used for teeth whitening. Will it affect my teeth negatively in the long run? If I whiten my teeth again after 6 months to a year when they turn yellow again, repeatedly doing it, is it harmful to my dental health in the long term? Is teeth whitening bad for dental health?

3. What are the side effects on the teeth? Is the sensitivity quite severe?

Are there different types of teeth whitening? Please tell me the pros and cons... Also, what are methods that do not affect dental health!!

Please let me know if there are any other important points, helpful tips, or useful information I should know...