i18N concepts

• What is the difference between Unicode and UTF-16?
• What is the significance of UTF-8? When to use it?
• If Chinese characters are represented as 2 or 3 bytes, how will you find out the length of a string in Chinese? For e.g. for validating the length of a field on a form.
• When do we need to use Base64 encoding?
• If I need to make an application i18n enabled, besides label/message strings, what are the other areas (data-points) I need to take care of?
• Can you open an unicode file (containing CJK chars) in notepad? If not, then why? What editors support unicode on your desktop?