Max Shutter speed
Nikon 1 J4 can shoot continuously at max speed of
60 fps and has max shutter speed of
1/4000 sec. 1 J4 also has an electronic shutter which can shoot silently at max speed of
1/16000s. One thing to keep in mind is that electronic shutter may cause rolling shutter / jello effects, and also banding issues under artificial light on your images.
Flash
Unfortunately 1 J4 doesn't have an external flash shoe so you are limited with the built-in flash.
Focusing
Nikon 1 J4 features both Contrast Detection and Phase Detection autofocus (AF) systems which ensures speed and accuracy of focusing in most situations. The AF system has 171 focus points and 105 of these sensors are of Cross-type. Cross-type sensors locks focus faster and more accurate compared to single type sensors. Nikon 1 J4 also features
Face detection AF where it intelligently detects the faces in the frame and locks the focus automatically.