How to change the font and colors of the wavy banner on the homepage

You have to use Custom CSS for that task:

New font family, font size, and different color

.clip-style1 text, .clip-style1 textPath {
  font-family: Tahoma, sans-serif; font-size: 100px; color: #FFF; fill: #FFF;}

Background color (from solid green to transparent black)

.clip-style1 .waveClip {
 stroke: #000000b2; }

You can use RGBA colors as well, not only hex colors.