That is a very subjective decision to make and hints that the whole issue is one of semantics. Many, many (but certainly not all) of the "nondenominational Christians" are the most Protestant congregations out there. In fact many of those churches were formed by orthodox Protestants fleeing their now liberal Mainline denominations for a completely Orthodox, bible based, nondenominational Church. They are congregationalists and from an ecclessiastical standpoint are almost identical to Baptist churches.
Indeed.
There are actually Independent Presbyterian Churches out there. They hold to the Westminster Confession. I would say they are Protestant in the pure sense of the word. They protested liberal Presbyterianism and at some time broke away. I know of some that have aligned themselves with Conservative Presbyterian denominations.