i think the difference between ozonating 8 oz or one liter is not that much. you may want to go an extra five or ten minutes on the litre.
as far as adding minerals go, you can experiment. there are different theories about this. i have ozonated water that i have added a bit of Sea Salt to. i also have added some active liquid minerals. it seems to me that the minerals trap the oxygen in the water more affectively. and i don't worry about weird chemical reacions because minerals and oxygen work synergistially together. but others only like to ozonate pure distilled or spring water. so its up to you.
usually when i buy a gallon of spring water i add a bit of Sea Salt , and a splash of acitve liquid minerals to it. then thats the water i use to ozonate with.