I prefer my soup to be on the salty side; I ended up adding around 6 tbsps of fish sauce. You can reduce the amount of fish sauce added to the soup though, especially if the fish sauce that you are using is quite salty.
Some people don’t add sugar to the soup and instead prefers to rely on the sweetness of the saba and the sweet potatoes. Sugar is optional but in my opinion it compliments the fish sauce quite well.
Most Filipinos use fish sauce and some calamansi (lime) as dipping sauce for the beef.