the HOB is not necessary, and will only serve to provide surface water movment which is good for O2 exchange. It can also be used to house LR, that is not in the display.

A small skimmer would be a good addition, in place of a HOB.

If you are not planning to grow corals, you dont need the blue light. Coraline seems to be pretty tolerant to low light so you should be okay with the low light. Other form of algea will be an issue, although the skimmer will help some, by removing some of the organics.

Normal Output florecents would not be enough to grow corals in my opinion.