Dimaggio,
Good questions.
1]Yes, you should feed the DSB, minimally as the benthic creatures won't need a lot of food, esp. at first when just getting established. You can then track ammonia, nitrite and nitrate levels as they spike in turn. When nitrate levels drop to zero, your system has "cycled" and should then handle the gradual introduction of livestock. Any other significant additions of LS or LR may cause the tank to cycle again. The resulting spikes in ammonia and nitrate will be stress factors on the fish, so it's not recommended if you can help it.
2]the creatures that will do poorly under NO light are photosynthetic ones, such as any corals or anemones that may hitchhike in on the LR. Most of the infauna [creatures living in the sandbed]don't require large amounts of light, so you should be OK there.
all the best in your endeavor,
-rw