After shooting a few dances in low light with the D3300 and 35mm, here are my views on the combination
. Though zoom may involve lesser moving about, a prime prompts you to be on the move constantly, hence you get better angles. A fast prime also means lower ISO and lower flash power.
. The inbuilt flash is good enough.
. ISO 400 works the best with minimal noise as long as the distance for flash is 3-4 meters
. F1.8 gets excellent results, as the flash strobes the scene to freeze it. It also isolates the main subject from the surrounding.
. With 24MP to play with, I generally focus on the person's face and ignore the distracting surroundings. There is plenty of leeway as even a 3 x 2K crop needs only 1/4 of the sensor area.
I have tried bigger shoe mounted flash - SB800 with diffuser or angled light, but that is cumbersome and heavy. The D3300+35mm is an extremely light weight kit so you can hold it for hours at odd angles without tiring out.