One piece to choral counting that I have found to be important is the connections that can be made between different choral counts.
For example, this was an eye-opening choral count for some 2nd graders. We began with the confidence builder of counting by 5s. We broke it down by looking for patterns. A lot of good talk and discussion here, but it really kicked up a notch when I challenged them to count by 5s off-decade. We began slowly, but then the students were able to idenify patterns and get going. We looked for patterns in this count, too, and then I pulled the two counts up side by side. The ahas! that the students had were quite exciting! So important for students to make these connections.
I did another one recently in a 5th grade classroom where we counted by 21s.
Students stepped up to the challenge of counting by 21s and looking for patterns. But the real excitement came when I asked them to do another count by 2.1. (I had copied the first count onto a clean page before we had found its patterns.) Students kind of gasped, but then I pulled up the clean screen of our previous count. They counted by 2.1 as I added decimal points into the numbers. When we were done, we made connections between the two counts and place value. We also discussed what would have happened if I had asked them to count by 210. These place value concepts were things that they "knew," but when we put it on paper, it really clicked for them!
Because I am in and out of classrooms, I did these "double-counts" in one session making the choral count a little longer than usual. I certainly think that it would work for a teacher to do one one day and the second one the next day. The importance is the time taken to connect the two counts, and following-up in later days with similar counts in order to help cement the counts into students' minds.
Beginning with choral counting is your first step. Give one a try! Once you get past that hurdle, you will feel more comfortable moving into a double-count!