What are the advantages of an online kitchen design service over simply calling somebody in to do it for you? Cost is one benefit: it is a lot less expensive to do it yourself online than for somebody to come to your home and do what you could do just as easily yourself. Another benefit is that you get exactly what you want, and you can't blame anybody else if it is not to your liking.
The place to start when you are designing your dream kitchen is with a dimensional diagram of your kitchen space. On a large piece of graph paper, draw the outline of the kitchen space, including any doors or windows that you will have work around while you design your kitchen. Accurately mark where your plumbing and electrical supplies are located. You can move plumbing and electrical supply points, but this involves more time and money, and it is always easier to accommodate existing service supplies into your design, if practical.