Your corrections, per current Church teaching are correct. However, each individual priest can decide whether or not he wants females in the schola or not. Some traddie communities do. Some do not.
I am aware the Pius XII made this change. I believe, however, it is still within my rights to argue as to the prudence or imprudence of allowing women to sing; however, of course, this would not be binding in any way.
I believe that the correct term to be used for laymen is "apostolate," not ministries, at least according to the Second Vatican Council's Decree on the Apostolate of the Laity. I believe the term "minister" and "ministry" is reserved to the ordained, per a document issued by the Joseph Cardinal Ratzinger.
I have forgotten the precise canonical language and reasoning utilized to arrive at 'altar babes' from female choir members; your terminology is fine.
The difference is between a 'formal' office and an 'informal' service. Altar girls and female choir members fall under the latter category, at the discretion, yada yada, etc. ad infinitum.