Jean, I play The Godfather Theme with no tempo in the first part adding a slight feel of rhythm for the second. The style is slow, no instruments acmp. except drums and bass. Maybe a tease of piano or guitar.
The beauty of this song is in the melody of the song and instruments you select. -- and the instrument changes you make. I feel you have selected a good song for a concert. as long as you treat the song with feeling and variations like a true artist.
You have an opportunity to express your feelings, treat the song with a clasical flavor. The stlye is of little value. just a slight feel of rhythm is needed. I do you use sounds in my left and right hand to complement the song.

IMHO, John C.