I don't take full choreography notes/blocking. The dance captain and choreographer have them, and I just capture key elements, such as the order that people come in, and where they're standing at key moments. When I am taking dance notes, I use blank paper and write out the counts on one line with the choreography underneath it. Ragtime really doesn't have much dance in it. The prolouge is crazy busy with movement and the Getting Ready Rag is real dance, but the rest is mostly just musical staging.
I wish I had great tips but I think what I do is a very personal solution that works well for me, but isn't very transferable.