Features:

The stars are finite in size because of finite resolution of the imaging system. They are actually unresolved.
The points on stars are part of star diffraction patterns in the imaging system. The overexposure of the stars brings out the points diffraction patterns which would otherwise be faint compared to the bright round part of the diffraction patterns.
The Pleiades stars themselves have a bluish glow around them because their light is being reflected from clouds of interstellar dust. Such reflecting clouds are called reflection nebulae. The interstellar dust preferentially scatters blue light.
The bluish glow is actually rather faint and a long exposure and/or high sensitivity was needed to bring it out. This, of course, means that the brightest stars get overexposed.
The 9 brightest Pleiades in apparent V magnitude (see Wikipedia: Pleiades: Brightest Stars) are named in the image. The Pleiades has about 1000 known members, but this number does NOT include unresolved binaries (see Wikipedia: Pleiades: Composition).
How many can be seen with the naked eye? Well this depends a bit on your particular scotopic vision and skill, and on the (astronomical) seeing. Most people under reasonably good seeing can see 5 right off the bat. Numbers 6 and 7 in apparent brightness are just a bit harder. After that it gets harder and harder. However, 14 seems to be limit for a skilled observer NOT making a colossal effort. See Sky & Telescope: How Many Pleiades Can YOU See? Bob King, 2014 October 22.
The 10 brightest Pleiades in order by apparent V magnitude: