Start with your connections. A 20 year career suggests you have worked with lots of people who respect you and trust your work.

Use them to test your market. Before making the move, send an email to coworkers you had strong relationships with (bonus points if those coworkers are nontech) saying you are starting your own consulting company that will build out sites/apps/tech. Ask in it if they know anyone they would introduce you to.

While I don’t think there is an answer other than “get lucky”, it’s important to get a sense what your early deal flow will look like, especially for financial planning.