Decide the Reading Distance First
Before anything else, work out how far away people will be and how fast they are moving. Everything follows from that.
For roadside and long-distance viewing, you get one message. Realistically that is a name and one word or number: what you are, and how to act on it. Anything more will not be read.
For close-range viewing behind a stand or at an entrance, people are stationary and can take in more, so a logo, a short line about what you do, and a website or phone number is reasonable.
If the banner has to serve both, design for the longer distance. A banner that works at fifty metres still works at four. The reverse is never true.