As a maker, I love it when the customer wants to be involved - to a point. Some customers want a knife "exactly like" so and so makes. Most makers, including me, will refuse to do that and tell you right up front that it will be close, but it will not be exact. Such are the nuances of the hand made blade and the desire for a maker to show a bit of his/her own unique style. Sometimes you will not be able to reach an agreement with a customer due to their demands or the incompatibility of the project with the maker's particular style. For example, I do not make knives with gut hooks. In those cases I politely tell him/her they will need seek another maker.
Few makers charge extra for taking on a custom order that is out of their normal line of work, unless the job calls for a difficult design, special tooling or unusual materials, however, they will often ask for a deposit. I usually have a customer make me a template out of mylar (the thick artist's stuff) or something similar. Even artist's cardboard will work and in at least one case, a guy sent me the design on a piece of graph paper. Sometimes it will take two or three renditions of the design and several telephone calls to get the project underway.
Search the web for makers in the Japanese style. You will need to find a maker whose style you like, then you can begin researching the maker.