Correct. Read the labels carefully and follow the instructions for re-coat times. The filler/primer is always sanded, and you should try to get a different color than the etch primer so you can tell where the low spots are. the filler will wet sand off and leave its color in the low spot. When you see this, stop sanding, and wash tank and dry, then spray another coat, let dry for appropriate time for wet sanding, and repeat. Most important to follow instructions for the product you are using. Try to get tack cloths and use them lightly after drying to remove any specks of dirt, hair, etc. between coats, and especially before finish coats, and clear coats.
Charlie