1) Yes, it would be correct to say that. In fact, Virginians understood May 15, 1776 — the day that their revolutionary Convention adopted a resolution calling for adoption of a written republican constitution — as the date of their independence. For more on this story, see Maier’s AMERICAN SCRIPTURE and my VIRGINIA’S AMERICAN REVOLUTION.
2) United in the war effort and in declaring their independence.
3) The union “as we know it” is unlike what it was 50 years ago, let alone 150 years ago. I don’t know what to make of this question.