Here's a scaled down standee. It has the same proportions as your 6 ft tall one.
Sorry for low resolution (=screenshots). But this is only about sizes.
The red texts are big because they are expected to be seen well from as far away as possible. They cannot be bigger because the lines cannot be longer. Some white around them is a must and some space must be left also for other parts.
The black title must be visible well at certain distance. Otherwise nobody will pay attention when they walk nearby. You must know how far people bypass it, but are expected to see the title perfectly. Make a test with a scale model. Have it on your screen say 3 inches wide and 9 inches tall. The model scale is 9in/6ft = 9in/72in = 0.125 = 12.5%.
Make it in your drawing program 9 in tall and zoom the view so that it's 9 in tall also as physically measured on the screen. This way your font size in the program presents also the actual size on the screen.
Let's assume you need good readability distance R. You should watch the 9in tall scale model at distance 0.125 * R. Let for ex. the wanted R = 30 ft. Then your test watching distance should be 0.125 * 30 ft = 3.75 ft = 45 inches.
Let's assume you find that title font size P in the scaled model fulfills the requirement well. Then real font size F = P/0.125 is apparently as big at distance 30ft. In my scaled example the font size is 16pt. If that's good seen from 45 inches away you need F = 16pt/0.125 = 128pt.
If possible the size should be so big that the existence of readable text should be seen also if the sight is directed say 30 degrees off. Make of paper a 30 degrees wide angle to test it. A person may not turn his head if he doesn't see there can be something interesting. The big red shapes on the top help this.
The general formula:
The height of the real standee = H
The height of your scaled model on the screen AND in your drawing program = S
Required good readability distance of a text = R
The test reading distance of the scaled model = (S/H) * R
The found good scaled model font size in the program = P
The needed real font size for the same apparent text size F = (H/S) * P or as well F = P/(S/H)
If the title catches someone's attention he probably walks closer to see the details. You must decide how close he really bothers to come. From that distance he decides if there's something actually interesting. This gives probably a smaller R to calculate the minimum font size for the body text.
