My Thai partner (male) is about to open a small business doing floristry and events. He has long experience in this field and has run a similar business in Aust (he has duel citizenship) as well as working in 5 star hotel in upper management. He wants to make a flower school and English school (with me as only teacher). If I was a partner in the business would I have a permit to work or can he open a business and employ one foreign teacher?

He needs to employ two additional Thai staff for him to be able to employ you or for you to be working as a manager there.

I believe the rule for having just two Thai employees for one foreigner is for people that is legally married.

Otherwise is four Thai each foreigner.

ok, what if we were a business partnership for a florist and language school (not just me being employed by my partner's school). Would being in a partnership (business) give a yearly visa?

Yes, if there are enough Thai employees and registered capital in the business allowing you to be employed.

In addition the company need to exist for at least 2 years because the company will need to show tax papers.

wouldn't being a partner in a partnership at least allow a yearly Non Immig visa?

Investment requires an investment of 10 million baht and can only be invested in certain things.