In the 30 I have a 4 line wrasse, a royal gramma and one purple fire fish that get along and give some nice contrasting colors. Of course I have to thave a fish fence around the edges though. I believe you have a three sided canopy. I would recommend some loosely applied gutter guard along the back regardless of the species of fish you buy.
Small anthias will be fine. Anthias are active swimmers but they can do well in limited space; they rarely do fast bursts but rather mope around at a leisurely pace.
so now the question.. how much "fissage" can i afford in my cube? I have about 70g of total water volume and run a octopus recirc 150 rated for around 180g. Can I have a fairly moderate load?