Entered once. Copied onto each plan when you save, so changing your weight later won't rewrite plans you already made.
Sweat rate is the widest-variance number in the model and the one worth measuring: weigh yourself before and after a one-hour ride, add back what you drank. Every litre lost is about 1 kg.
Scan a barcode, type a product name to search, or just fill in the numbers yourself.
Name, carbs and weight are enough. Sodium helps the plan tell you whether you're covered on salt.
Drop in a GPX, or paste a route link, and distance and climbing get read from it.