There are many resources to help you with your business plan. SCORE is a mentoring/advisory service that is free. Their network is really extensive and have many professionals that are either retired or philanthropists that are looking to give back. Free Small Business Advice (https://www.score.org/) They are a great resource which we also used to help us build Umergence. Simply put in your location and they will assign you to the nearest location they have for that area. Provide a bit of background and they will find you a SCORE mentor that has expertise the area of your business.
You can publish your business plan and crowd source opinions from the Umergence community. The community is comprised of your potential consumers and possibly investors who can help you raise the capital you need to build your business. With your idea validated by the community you reduce your risk to bringing your idea to market. Publish each section of your business plan and the community will have the ability to add comments to each section of your business plan. Then each comment can be up/down voted so based on the voting you can use it to gauge and improve on your business plan. Wishing you many successes!