Depends if you want a clear dry sake or a semi-sweet to sweet rice wine. Check the two threads at the top of this forum area on Rice Wine and Traditional Sake. You can simply scale your recipe to suit any size batch. IMHO, start with the rice wine at a one gallon size until you perfect a batch or two, then step up to a five gallon batch once you have the steps and ingredients down. Traditional sake is a little more exacting, time and labor intensive and might require more effort/time/steps than you're willing to give it. For example, i've got three batches of rice wine under my belt and i'm about 1/3rd of the way into my first batch of traditional dry sake (i'm about fifteen days into it and just finishing up the traditional starter). Sake-making also requires precise temperature control and the yeast used with it is a lager-type yeast. It MUST ferment cold to avoid the tropical fruity flavors so prevalent in rice wine and for that, you'll need a fermenter with an external temperature controller such as a drop freezer.
The cool part is even though Rice Wine and dry Sake are different, they're both good in their own respects. Choujiu (rice wine) is a milky white wine with an ABV hovering around 20%. It's very light and sweet to semi-sweet with tropical fruit flavors that taste like kiwi, star fruit and strawberry starburst with an alcoholic note. You can pasteurize it at any stage you like or let it sit in a bottle for a few days before pasteurizing it to produce a carbonated rice beer.
The trickiest part of it is finding the yeast balls, but if you have an Asian market or two in your area, you'll probably be able to track them down.