Diet: what can be a reasonable amount of carbs in mgs. for breakfast without over doing it in a healthy adult?

None needed, liver: very good at both releasing glycogen & converting protein & fat into sugar, smoothly compensating/preventing drops in glucose, very effective for keeping blood glucose in healthy ~70-120 mg/dL range. Reasonable is a viewpoint & highly dependent on individual status & situation. If slender, very physically active & usual blood glucose values low normal, can tolerate more carbs with ↓odds problems.