I always found that whenever i put into single pots immediately, that the seedlings always lingered and grew much slower than when I clumpped them.
Rotting...that is one thing with brachys in general. they can rot VERY quickly.
It depends on the cross, as far as leaf span. I have some that only reach about 4.25 inches while others are around 8-9 inches. How many sets of leaves do they have?