How much “compounded” asafoetida to use

Yogurt and milk might work, but those ingredients are not in authentic chapati. When I hear the words "hard" and "rubbery" in reference to pan-fried bread, I'm almost certain that the problem is that they are cooking for too long on too low of heat. Increase the heat on your pan (it should be very hot) and cook the chapati very briefly on each side. This will still give them a nicely browned exterior, without turning them into sheets of rubber.

In theory chakki is a flour mill, and chakki atta is flour fresh from that mill. Realistically of course nothing you find on your grocery store shelves is fresh from a mill.

Atta flour is made from hard wheat, which has a high gluten content. This means that your flour is probably better for bread than typical all-purpose whole wheat flour from the baking aisle. If it is hard white wheat this might explain the color, as ground white wheat doesn't look that much darker than all-purpose flour.

Like typical grocery store whole wheat flour, atta flour is coarsely ground. This may give your bread a more grainy texture (not a bad thing), and makes atta unideal for cakes, biscuits, and quick breads unless you like them with a coarse texture in the crumb. If you would like to use whole wheat for baking other than bread, whole wheat pastry flour is the usual suggestion (or grind wheat yourself to a very find grind).