What is the number of decaps used in each power pin?
It is generally recommended to have decoupling on each individual power pin.

If two pins are next to each other or very close then you can also let these pins share the same decoupling capacitor(s). But if there is enough space on the PCB, the preferred option is still to have decoupling on each individual power pin.

It is also recommended to use a small value (100 nF for example) capacitor and a large value (1 uF or larger) in parallel to get better decoupling. Why this is so is explained by Dave in this EEVBlog video.

It is recommended to place the small value capacitors as close as possible to the IC's power pins. The reason for this is to keep high-frequency loops small to minimize supply ripple and RF emissions (EMI). The small value capacitor works better at high frequencies so its placement is more critical.

You can compromise on the large value capacitors and place fewer of them and only place them where it is convenient.

Decoupling (or bypass) capactitor selection isn't an exact science, most experienced designers just follow the basic rules as stated above, look in the datasheet of the IC what is recommended, copy what is done in other designs and use common sense.