Maybe you should post some pictures of a few pieces that you've completed, so we can get a good idea of what a good 5 years is. Not to mock but 5 years at 40 hours a week is vastly different than an hour a week. Will you be doing any fine embellishments such as engraving, inlaying, stonework? Working knives or mantle hangers?
To the question, ultimately many customers won't have "blueprints" for a knife, and you must also be the creative consultant and artist in most cases. People mainly have an idea of what they want, but rarely have a concrete design drawn. There is clearly a market for custom knives as that's what this forum is about! Being a maker means you can choose commissioned work over selling a set of models, but comes with its own set of challenges when making things "perfect for the customer" in all aspects of the knife... For EVERY knife. That means you will be doing a lot of drawing and discussing with customers, which is fine, but takes away from time you could be making a knife for sale to the public as an entirety. Even if you don't have "models", just make knives to your pleasure and put them up for sale. Reputation is everything when you get into the realm of full blown one off customs. Those customers are typically very discerning and the internet will likely pull up other makers before yourself for that type of work without lots of ad dollars. Just being honest, but the good news is selling great knives and being a part of a community such as this is a great way to build a reputation!
This is a fine community, and often I find it is far more helpful than mocking. But listen to most makers that do this full time, and you will soon find out that doing one off customs is a small facet of many skills they possess, and use, to make money. Sometimes our plans are more grandeur than they truthfully are, unfortunately.
As they say, if you wanna make a million making knives... Start with two million!
Regards,
Justin