The needs of a church differ. You may find that your church's choir can function without a president.
However, if there are a lot of business details that must be handled a president can be quite beneficial. The MOM can focus on the music and spiritual matters of the choir. As MOM the business of the choir is still your responsibility, however, with a president, you will have assistance so that you can concentrate on the other areas I stated.
As far as proper orde, chain of comman, get with your Pastor. No one hear has the authority to tell you the chain of command at your church. That is usually set up by the Shepherd (Pastor) of the church.
At my church it was Pastor>MOM>Choir President.
Musicians & Choir Directors were responsible to the MOM. Choir officers were responsible to the Choir president, who was responsible to the MOM.