Question

2) How does the clumping of dark matter differ from the clumping on luminous matter?

Answer 1

When a luminous matter contracts or clumps due to the gravitational pull of its own, there are random collisions as the atoms get close to each other. These collions then cause the loss of energy mostyl in the form of heat and the contracting body is cooled. This further aids the contraction of the matter and the process is continued until no more clumping is possible and forms gas clouds, stars, planets etc. This is because the luminous objects interact both gravitationaly and electromagnetically.

Whereas on the other hand dark matter is believed to interact purely gravitaionally, except some theories which take into account weak interactions. Suppose the matter is falling under gravity and are accelerating, but since they don't interact, there are no collions when then try to clump under gravity, so they just pass through and extend until it is pulled back again, causing an oscillation sort of. Since they don't collide to loose this energy, this keeps happening.

P.S:

Further if interested look at Dark Matter Halo.