When did I officially start my home-based (sole proprietor) business if I began purchasing supplies in Sept., 2020 but sold to my first customer in 2021?

This confectioner business will be on a cash basis. I am working from home. In Sept., 2020 I purchased supplies where I keep them in a dedicated space in my home.  I made many chocolates to practice and give away for sampling in 2020.  My first sale will be in April, 2021.  #1. When did I officially begin my business? #2. In which tax year should I claim the supplies? (I will be operating on a cash basis. No major purchases were made in 2020.) #3. In which tax year and in which month should I deduct expenses for my home-"office"? Thank you!