Add small pieces- it’s always better to add more than have to take some away, don’t add big pieces then realize your braid is too fat and have to start over. Add small pieces till you get your desired size pertect braid.
Adding product- yes you add product to the root of your clients hair, but after the braid is started you also have to add product and detangle the hair as you braid.
Braid tighter- starting the braid doesn’t have to be too tight, you don’t want your clients in pain. But once you’re off the root, tighten your braiding methods little more to get that uniform/symmetric braid every time.