英语演讲这样开头行不行??

Hi 很不正式，最常用的是hello.
或者是：

Good morning, ladies and gentlemen.女士们，先生们，上午好。

It's too informal.
Maybe you should say is like this:
Good evening, everyone. I'm very glad that I can stand here to give my speech. Today, I want to say something about Jay Chou.

你也可以根据时间的不同来开头
如果是晚上,你可以说..Good evening , everyone.

Today I will tell you something about Jay Chou
最好改：Today I am going to talk about Jay Chou with you.这样更加亲切，与别人交流．

可以．很好．

why not?