[1] It is caused by a Doppler shift associated with the random peculiar velocities of galaxies bound in structures such as clusters.
[2] Depending on the particular dynamics of the situation, the Kaiser effect usually leads not to an elongation, but an apparent flattening ("pancakes of God"), of the structure.
[4] ISW arises because large-scale gravitational potentials are decaying in time (due to dark energy), so that a photon passing through a low area of gravitational potential gains more energy on entry than it loses on exit, making the background galaxy appear closer.
Gravitational lensing, unlike all of the previous effects, distorts the apparent position, and number, of background galaxies.
The RSDs measured in galaxy redshift surveys can be used as a cosmological probe in their own right, providing information on how structure formed in the Universe,[5] and how gravity behaves on large scales.