I do not think there is a correct answer to your question. It is a matter of taste and goals. What kind of juice are you planning on using? If you are planning on White Grape Juice from the grocery, then 2 quarts is probably plenty unless you really want a country wine type of mead. If you are using a good wine grape juice then 2 quarts would allow the fermented honey to dominate with more subtle wine flavors. Using all juice will give you more wine flavors than mead. Or you can try something in between. All are good. What do you want?