Since you asked in English, I'll be replying in English. If you can't understand something just let me know.
5. 'Listen to music is good for you, singing alone won't hurt."
The first part of this sentence is wrong, it should be "Listening to music is good for you." The second part should be "singing along won't hurt" which means, if you listen to music 听音乐 and sing along 一边听一边唱 it won't hurt 不会妨碍你的.
6. "Had not better I" and "Had better not I" are both grammatically incorrect - don't ever use it.
"Hadn't I better" is the correct form.
Hadn't I better keep going?
Hadn't I better continue practicing?
7. "Wait til u are more satisfied, it is better to be content than sorry"
This is similar to the phrase "better safe than sorry." It means you should wait until you are 100% sure of something, so that you will at least be content with the result.
8. "You'd better" sounds more commanding, so you shouldn't use it against your elders ."It'd be better if you do" is more polite, so yes it is more suitable.
9. "I dare say" and "I daresay" mean the same thing.
10. No, you need to say "Yes, you need to." Just saying "yes you need" is incorrect.
Hope this helps. ;)