I wrote grammatical corrections in red and stylistic suggestions in blue.

teachers' day host words

Ladies and gentlemen, good afternoon.
There comes the Twenty-seventh Teachers’ Day is here. Dear teachers, on this particular day, there is too much we would like to say to you. We always thank you! You are so hard (I don't know what you mean by "hard". Do you mean that the teachers were strict?)!
You are the first breeze in the spring; you are the first nectar in the summer; you are the first sunshine in the autumn; you are the first snow in the winter.
You are the candle; burn yourself and light the others. You are our second parents and so kind to us.
We will never forget your words. You taught us so much knowledge (you could say "you taught us so much" and leave out "knowledge", or you could say "you gave us so much knowledge". It is usually not correct to say that someone "taught" you "knowledge".) and taught us how to be good people.
There aren’t any words that can express our thankfulness.
So in your festival, we wish you happiness and all wishes come true (you might say, "and we hope that all your wishes come true" or instead, you might say "we wish you happiness and all the best").
My friends, thank you for your participation. Although the singing and dancing are almost over, but we will respect and love you forever. Let’s clap our hands to celebrate teachers’ day once again!
Ladies and gentlemen, it’s time to say goodbye!
Thank you for coming! I wish you health and happiness!