The balloon gets you looked at. Whether anyone can read it is a design question, and it is the one most people get wrong.
Three words, maybe four
At 120 feet, seen from a moving car, you have about two seconds and a surface that is moving slightly.
That is enough for a name. It is not enough for a name, a tagline, a phone number and a website. Every extra element makes the important one smaller.
The blimps that work carry a business name. The ones that disappoint carry a paragraph.
Contrast beats colour
Dark on light or light on dark. That is the whole rule.
Against a bright sky your blimp is effectively backlit, which flattens mid-tones badly. Two colours that look distinct on a screen will merge at distance. Red on dark blue is a common and expensive mistake.
Heavy type, no fine detail
Use a bold weight. Thin and elegant becomes invisible at distance.
Avoid fine outlines, drop shadows, thin script and small registration marks. They will either vanish or turn to mush, and neither looks like the brand you approved on a monitor.
Two sides, two messages
A different message on the second side is $125. Worth it when the two approach directions genuinely need different information, and a waste when they do not.
Extra colours are $109 each, covering both sides. Letters over thirteen per side are $6.50 each, which is another reason to keep it short.
More at arizonaballoon.com.