Scales are useful for keeping track of weights, not just of your snakes but also of the prey you are offering them. A general rule of thumb is a prey item that is 10-15% of the snakes weight. By using a scale you can keep accurate track of if your snake is gaining weight or losing weight, as well as making sure you are giving your snake a meal that is appropriate for their development level.
Personally, I would keep him to a 5 day feeding schedule. That's the feeding schedule I use for my hatchling. She went on a three week eating strike when she first came home and is now doing fine, pushing 150g and getting ready to move up to the next size prey item.