Mold should be dealt with immedeately as soon as it is discovered. Otherwise, it spreads, builds airborne spores and can become a health hazard. It also damages the building. Small affected areas can be removed fairly easy with a mold removal set.
Not necessarily – above 60% relative air humidity, the cardiovascular system is noticeably more strained. Also, it provices a climate in which mold can thrive. A hygrometer enables you to monitor air humidity. If it is too high, you can lower it using a dehumidifier.
That would be nice. Unfortunately, mold is fairly robust and can withstand high temperatures, long periods of dryness, and it can even endure exposure to many chemicals. It has to be removed manually, e. g. with a mold removal set. If the contamination has progressed too far, a professional should be hired.
Quite on the contrary. With tilted windows, the air exchange is taking rather long, whilst cooling down the wall around the window significantly. That's where water condenses, forming water droplets. Better air intermittently with windows wide open. Ideally, open another window or a door on the opposite side of the room too, so the air can blow through, allowing the room air to be exchanged swiftly. If that is not sufficient to regulate humidity, consider purchasing a dehumidifier.
No, newer and renovated buildings can also be affected by mold. If the air humidity is too high for prolonged periods, it's just a matter of time until mold forms somewhere.
Potting earth can indeed become moldy, but most of the time, the white layer coating the soil is just chalk remains from water with a high mineral content ("hard water"). Chalk on potting earth tends to be thin and hard, and it crumbles on contact. Mold, on the contracy, is usually soft and "hairy".
Soil with a low turf content helps preventing mold growth in flower pots. More on moldy potting earth
Unfortunately not. What does help: Chlorid spray, concentrated alcohol or hydrogen peroxide.