Do you live in Olsztyn? Are you Polish
Yes. I live in the beautiful city of Olsztyn. Somewhere between fifteen lakes.
Do you know the answers to 1 & 2?
Sorry. I don't know. See zielonalinia.gov.pl/temporary-residence-and-work-permit-41713
So I can buy a flat but not land and build a house? I think I read somewhere that I need to get a special permit/permission to buy land?
Yes you need to get a special permit/permission to buy land (especially agricultural land)