I prefer the air stone, at a lesser volume then you have in #52, over the HOB filter. Filters are not necessary. A strategically placed sponge filter is also fine. The currents created by the air bubbles seem to have no impact on shrimp. The air flow rate can be reduced when zoaea are present. The finer the bubbles the better. Do not over populate. When the opae ula begin to breed your population can easily triple within a year. When they start to breed there seems to be no end.
Where are you getting the extra 100? I am looking for opae ula from the southern big island or from another island.