These are all common questions posed by piano owners.
Pianos are mostly wood and are greatly affected by seasonal change.
Variations in the air's relative humidity, and to a lesser extent temperature, cause a piano to go out of tune. In the long run, repeated swings in relative humidity can cause damage to the finish, cracking of the wooden soundboard, and even structural failure. So, when locating your piano, try to choose a spot with the fewest drafts, no direct sunlight and stable temperature and humidity. Common lore says that a piano should always be on an inside wall. This is not necessarily true.