1. If I establish Spółka z ograniczoną odpowiedzialnością in Poland (being a foreigner) - what will be the taxes?
2. Is that true that in this case I will obtain "karta stalego pobytu" ?
You'll still owe taxes to the country that you're resident in. Living in Poland won't change a damn thing.
No, you won't get a permanent stay card. You'll be able to get a temporary residence card for 1 or 2 years, but that's it.