Their legs continue to grow for a long time so you have to regularly monitor and replace leg bands of any type, including zip ties. I agree with you on those bands, what size do you buy. I eventually wound up using zip ties but only on older birds. That got me the information I needed. Your situation is different.
Instead of bands on their legs when they are chicks you might consider painting them. I don't mean spraying them with enamel. Many hatcheries will mark a chick with food coloring to identify them if you are ordering similar colored chicks. Depending on the color of the down or feathers you might work out a marking system to identify them. A certain color on the forehead could be one chick, a different color on the forehead would be a different chick. A mark on the right shoulder could be a different chick than one marked on the right shoulder and the left rear with the same or a different colors. You can combine different colors and body locations to identify a lot of different chicks.
Chickens shed down and feathers pretty fast as they grow, you will need to keep up with your marking system. That's not just one or two times as they grow, but several. Instead of food coloring you might use different colored Sharpies. It will not hurt them, you are just coloring some down or feathers.
If you get careless and don't keep up with the leg bands you can hurt them. If you don't keep up with the coloring you do not hurt them, you just can't identify them anymore. I think paint is safer. Another advantage is that when they are sitting down or not in the right position you can have trouble seeing leg bands. I have that with my hens when they are on the nest laying an egg, I can't see the zip ties on their legs. I have to work harder to see which pullet or hen actually laid that egg. You might be better able to identify them as chicks if you use colors on body parts.
I don't do paint as I don't need that information. You might want to consider it.