Personally would add all in one shot to prevent territorialism. Whatever you may put will be well stablized in the tank and may show some aggression towards new addition down the road.
In 55G, am sure could have 2 pairs. If one pair starts to spawn, may want to set up breeding tank as they becomre more aggresive, not just towand themselves but towards other fish which may come close to thieir turf.
If happens to see tankful of
GBR at
LFS, watch them for a while (have sttod in front of gbr tank for more than 30 minutes to pick out mated pairs). Should be able to pick out few mated pairs. Pair will constantly chase others trying to protect their turf (even very tiny turf), always returning to each other and turf after the chase.