Go to your local home center. Your door opening is a standard size. There are several styles of bifolds available and they all come with complete hardware kits. They will have everything you need for trimming out the opening also. Just ask.

With bi-fold doors there is a small track on the bottom that you screw into the floor to put an adjustable peg into- to keep the doors from swaying and you can vary the height. The track is only about 4 inches long and is as wide as the bi-fold door. For molding, treat it like you would an opening from one room to another. Trim it out the same way using the same materials.