How can I know or get to know about this? Which Urzląnd's are involved?
Urząd Miasta - Municipal and Communal Office
but make them send all mails to my country's adress instead?
Offices don`t send emails, they send notices by regular post if there is a problem. The only exception was pandemia quarantine.
You mentioned removal of snow in winter. You will need sb to do it for you. Can`t that person collect your mail, too?
Can I set any czynsz I want or are there any limitations?
Yes, any you want.
Yes, you have to pay taxes for letting your property, it is natural.
As for heating, it depends on a winter - the last one was very mild - the temp in my summer house was always around 10 degrees C.