For an online business, a detailed and in depth business plan is usually not necessary unless you are trying to combine your online business with a traditional business. For most online business startups, the detail involved with planning a traditional business is not required. However, it would still be beneficial to you if most of the topics were still covered, even if only briefly. Having a written plan in front of you will help you to focus on important aspects of the business.
So, although a detailed business plan may not be required for an online business, I am going to include it here so you can at least look at and consider each section and determine yourself if it applies to your business.