I've used both fish food and ammonia. For fish food, I used an amount that was equivalent to the size and quantity of fish I planned to put into the tank--at the time they were going in (not when they were full grown. Small fish = small food.) Ammonia is more accurate, but if it's food, just don't "over feed." For ammonia, there is a sticky on how much to use (although when I was doing it, there wasn't information, so I just dropped a cap full in each day.)
I don't recall it smelling bad from food or ammonia, but I like the way a tank smells even after feeding, so I guess my opinion isn't going to help much.
You don't have to add a lot of stuff since the bacteria population will grow as your fish grow. You just have to have enough bacteria to match the size of the fish at the time you put them in the tank and then when you get the fish be careful to slowly increase the amount food you feed.