For flash effects, the cast shadows, shadows and lighting are very important, your light values are too dark, your shadows are too soft and some too light, you need to have cast shadows, so I suggest looking up references of flash photography and also illustration that mimic it. I tried to add them in but I don't think it turned out that well. This scene has a lot going on so I suggest simplifying it if possible, there are 5 characters in this scene, some with complicated outfits, a more spacious setting and with the flash effect on top, each character is effected by different amount of light based of how far they are from the light, not to mention the direction the cast shadows they (including things on the outfits) will cast. You will need to have a strong understanding of perspective so that you can at least estimate where the cast shadows will land on the wall, ceiling and other objects that are in the way. You can try to use 3D models to help but I still highly recommend studying perspective. Also do more study on anatomy so that it's easier to know where the light and shadow will hit on which plane of the body and also make the poses feel more natural. For the extra effects, you can add chromatic aberration and some noise to give it a more "photo-ish" vibe. Overall, this is a very ambitious piece, but with the right knowledge and understanding I think you will have the outcome that you are more certain and happy with. Good luck!