How much to water a single seedling?

Hey there JR420! Personally I would do a half cup and check dryness daily. Once the seedling stage ends typically It depends on the container. It looks like you are going straight into the final container without transplanting. Unfortunately this will make watering difficult at first because seedlings don't drink much and the excess water will remain in the pot for longer than wanted. Be careful not to over water your plant because of this! I suggest smaller quantities due to the container size until shes able to drink it up!