When building a deck, always nail a thinner member to a thicker member. Hot-dipped zinc-coated nails are a good choice. For more holding power, consider using either ring- or spiral-shanked nails, or go with deck screws. If using screws, it's best to pre-drill pilot holes.
Most dedicated wood lovers insist that the best finish for a wood floor is a floor-formulated tung oil. Derived from the nut of the tung tree, tung oil penetrates the wood and bonds with the surface fibers. More giving than a synthetic finish, a tung-oiled floor will evolve with wear rather than cracking or chipping. Originally developed as as ship sealant, tung oil naturally provides excellent protection from spills, water, traffic, and dirt. Cleanup is simple, with a little clear vinegar in water or an oil soap mixed with water.