How can I start a self sufficient business after retirement?

Get help from a peer-mentoring group or new business owners. A small business organization has these groups. Talk about your challenges. Some people may have the same challenge. It is better to meet face-to-face, but now people have to talk online through Facebook or a video group call on Zoom or Skype.
Next for Career Pivot and Me are among the groups I recommend. Customer (desirability), infrastructure (feasibility), and finance (viability) are the three essential areas on which you need to focus. Write your ideas on sticky notes. To keep ideas flexible and moveable, finally do your research.
Follow your competitors to see what they say. You might cooperate in the future. What are the biggest challenges for entrepreneurs over 50? Finding finance is a big challenge, so investing your own money may not be much, but it is better than nothing.