If you want to use coral gravel use a fine grade. It will become live sand over time as you add live rock and invertebrates. Your powerheads should be located at opposite ends of the tank. Having them aimed towards each other will create dynamic water movement. Where you locate the water return from the sump is not critical.
Most systems return the water out across the surface.
I would limit the number of fish in your aquarium to about six. A tang is good for algae control. The Flame angel could possibly present some problems with picking on corals, and in many cases they are not long-lived in aquariums. I am not sure what this Pajama wrasse is but many of the wrasses are not suitable for reef aquariums. Low lighting reef aquariums would probably have multiple regular-output fluorescent lamps.