Unless you intend to prcoess a lot of film I would start with quarts, easier to mix quarts than gallons, takes less space to store, and although Df has long shelf life it will go bad. I have used Df for many years, when I was a working JP in the 70 and 80s always carried a quart Df kit a packet of dry fixer, and a small amount of a wetting agent to mix if I needed to develop and did not have access to a darkroom. I also used Df for several years when I moved to the desert as my water temps run 90 degrees F in the summer. I made a water chiller so now I can use a number of developers.