Some of the Adenium have grown much larger than others and it's finally come to the point where I need to pot up the largest. They still have relatively small root systems compared to what I was expecting. The biggest problem is that the large ones are blocking light from reaching the smaller plants. As such I'm moving up the four with the biggest leaves.
I ended up using a mixture of 1 part cactus mix, 1 part peat-based mix, 1 part aquarium gravel, and 1 part orchid mix. This is just what I had on hand, nothing special. As long as the soil is about 50% well drained you're generally good to go.
Last time I transplanted them they went into shock, went dormant for almost two weeks, and were attacked by mites. This time I didn't do it outside in full sun and gave them a good misting and soaking after. Hopefully they'll just keep on growing but if they do go dormant they're almost too tall to fit under the lights so it may be for the best (there's a lot of other short seedlings so I don't want to raise the bulbs). They should be good in these pots until they start flowering (and probably a month or two after).
So apparently my camera just decided to die so I'll upload some pictures after I charge the batteries.
Update: Charged! They look super lush from the top. You can really see how the larger ones were blocking the light.