Worst that can happen: You end up in exactly the same position you are now without the store business.
Set realistic goals for delivery dates and amounts. Leave yourself enough time to cover things like broken equipment, late delivery of your supplies, brief illness (a day or 2 with the flu could really slow you down), etc. As others have said, consistency is a very important thing in business. A supplier that meets deadlines is highly respected - far more than one that is sometimes fast and sometimes missed the mark.
Be prepared to speak to what you'll do for special orders, focusing on delivery and how the store will profit.