Originally, the polite form of "you" in English was "ye," and the informal form was "thou." Although "thou" may appear to be the formal version of "you" because it is often used in religious ceremonies and when addressing God (in the King James Bible), it is actually the informal form. As a Germanic language, Old English shares similarities with modern German. "Thou" is lexically similar to "Du" and "Ye" rhymes with "Sie." Note that French, German, Spanish, Italian, Russian and Scottish Gaelic (all of which maintain the use of an "informal" singular form of the second person in modern speech) all use the second person informal form to address God. So it is not particularly surprising that the King James Bible used the second person informal "thou" to address God as well.

No- modern English doesn't have a formal you. In old English there were a variety of words used for you such as 'thou' or 'thee'. However these words aren't used anymore. There are more formal/polite ways to structure a sentence. Often phrasing a command as a question can be considered more formal. eg. Can you pass me the salt Would it be possible for you to please pass me the salt. Alternatively using the passive voice is considered more polite. eg. You broke my bike My bike was broken by you. hope that helps

Yes, originally it was "thou", "thee" "thy" and "thine" (nominative, accusative, genitive, genitive adj.) You can still read in the King James Bible these forms.

Also, Timmy is right - both "you" and "ye" were the polite forms in the past. In modern English, we only have "you" for everyone. (Thought I would clarify that in addition to 'ye', 'you' itself was also the formal form. I guess modern English kept only the formal form for daily use).