your plankton is definately not pointless. Id continue feeding small amounts, watch the cycle, you can do water changes, the tank will possibly cycle more slowly, but if I were to do it again thats how I would do it... try to preserve as much life on the rock as possible... I woiuld even add light right away. Some will say dont add light right away as you could develop an algae bloom. I (personally) would not worry about that .. let the cycle go more slowly with water changes then deal with an algae problem IF it comes... You will have an algae issue anyway... just keep nutrient down via water changes with RO/DI
Just my 2c... keep us posted whatever you do.