The Big One: no, the initial post does not contain the basics. It contains many chumros. Can you find a mekor for everything that’s listed there?
Joseph: yes, tznius is halachah. The question is, how much is halachah, and where does it become chumros? Many things discussed in this thread are chumros, not the basic halachos of tznius.
Obviously, certain parts are basic halachah. A woman can’t walk around in the summer time wearing a bathing suit. However, some people are machmir to wear sleeves which go all the way down to the wrist. Others only cover the elbows. Still others have sleeves down until the elbows. Who are you to say what the basic halachah is, and where the chumros begin?