For Hello, usually we just use 你好 (ni hao) or 您好 (nin hao) (more polite)
How are you? - 你好吗? (ni hao ma) (Usually we use this)
- 您好吗? (nin hao ma) (This is more polite)
today - 今天 (jin tian)
So, for how are you today? - 今天你好吗? (jin tian ni hao ma)
But, in our speech, we usually will omit the 'today' , so just simply 你好吗 is enough already.
I'm good / i'm doing well / i'm fine - 我很好 (wo hen hao)
And sometimes, we will include thanks to be polite
- 我很好,谢谢 (wo hen hao, xie xie) means I'm good / I'm fine / I'm doing well, thanks
Hope this helps