In general, Adderall is not affected by food but there are some interactions that could affect the absorption of the drug. IN your specific case, Vitamin C and acidic foods (like fruit) can lower the absorption of Adderall (or amount that actually enters your body). As a general rule, take your Adderall at least 30 min after eating something acidic or a vitamin C supplement and don’t take the vitamin C or acidic food for at least 2 hours after taking the Adderall. If you take XR, I wouldn’t worry too much about the type of food intake later in the day.
Consistency is the key. If you have a routine, stick to it and you can take a properly adjusted dose accordingly. Work with the immediate release product twice a day for a while while you figure out how your dose is affected by what you eat and if what small changes (+/- 2.5 to 5 mg) can be done based on what you eat.
Overall, as long as you dont take huge amounts of Vitamin C, you shouldnt have to dose adjust based on your food choices. It is probably best to take your vitamin C at night or with dinner since you probably dont take Adderall in the evening.