Someone is joking with you. There is no way that you will be granted a visa and residence permit on the basis of having your own business without a proper work permit and full-time work contract.
The fact that the "school" wants you to open your own business is a sign that they are not going to pay you well enough to live. The fact that they offered you, a non-native speaker, a job to teach English in Poland, when there is no shortage of non-native speakers in Poland, is very, very suspicious indeed. Either they are totally incompetent, or they are a scam outfit, or both.
In any case, there is no realistic way for you to survive by teaching English in Poland. Or Spanish, for that matter. Forget about it and make realistic plans. Poland has nothing to offer you.