The First Amendment does indeed begin with the word "Congress," and the Tenth Amendment is a clear expression of the idea that the federal government has limited powers. The First and the Tenth are the bookends, and all of the rest of the Bill of Rights is sandwiched in between the bookends. Why is so hard to understand that all of the Bill of Rights were only intended to limit the federal government as well? Just because the words don't literally say so? Look at the first ten amendments as if they are a row of books on a shelf. The first book makes one point about the federal government's limited powers, as does the tenth book. There's nothing wrong with assuming that all eight of the other books were also intended to have the same limited meaning. And the historical context of WHY the Bill of Rights was proposed also supports that interpretation.
I see no reason to presume that to be the case. Each amendment of the Bill of Rights was adopted individually. Two of them were not part of the Bill of Rights at all in the end. It took over 200 years for one of them to be ratified. Another remains pending before the states, very likely never to be adopted. If you read the Bill of Rights as one volume, I'd say you have to read the Reconstruction Amendments similarly. I don't see many originalists willing to do that as it would grant Congress immense powers over issues regarding race.