For my mind Japanese gardens are not that difficult to build once good product has been achieved. What you need is natural product such as feature stonework and stepping-stones. You will need a lantern and that will have to be made of granite or some other type of natural stone. If you buy a concrete one you have failed already!
A water feature is nice if you can put one in but not necessary, if you do just make it natural and flowing. Plants to use will depend on where you live but Camellia, Azalea, Bamboo and of course a Japanese maple would be nice. Shaping a type of plant is important as it will give the garden a neat and cared for look. A Niwaki can be used and any tree from your local area is fine as it is not about the tree it is about how you would prune it into a sculpted tree.