On your first question, maybe a lot, maybe a little. Cannot tell without a lot more information from you.
Your first step is to understand the cause of the mould and then address the cause(s) to prevent a re-occurance. Do you own or rent the property. If you rent, then have you contacted your landlord?
The trigger for mould is available moisture. Most times the moisture source is condensation.
Insufficient heating (or ability to retain heat in the property), excessive moisture load (typical family can create up to 18 liters of water in 24 hours) and poor ventilation are the three culprits and generally it is some combination of these.
Having said all that, make sure you don't have any leaks or water ingress issues.
Do you have any images of the problem?