These all ring true in my experience too. One more thing I would add is to specialize if you can. Don’t try to be too general in the services you offer. You can greatly increase your own market demand this way.
The counterpoint is that it needs to be a big enough market and one that you can service. Another thing to be careful of is that markets move on. I've known consultants who were world experts in some company's products or specific technologies. And then that company or technology ceased to exist and they really weren't sure what to do with themselves.