this models are made specifically for games. you can use than anywhere as you like, this are low poly models comes under 2k vertices on etch models with 4k backed textures.
you can add text on the colour (albedo) texture for having text on your billboard model you can do that by using any software that you like. (ex. figma, luncy, photoshop, etc).
all models have thare own textures and fbx file. textures come with 4k size.