You cannot usually substitute balsamic vinegar for cider vinegar. The flavor profiles are quite different. However the chemical properties are similar, so the actual answer depends on the particular...
depends on what you are using it for. White vinegar is considered "light" in consistency and balsamic "heavy". Balsamic, if aged properly, can be almost syrup-like in consistency. So, it will depend...
You could, but the taste is going to be extremely different: not only does balsamic vinegar have a very distinctive flavour but it is also a lot less aggressive to the taste.