I would assume the reason for the need of the shadow mod is match the shadow with the new mesh the body mod offers (screenshoot in mod page shows some comparison).
That said, if ya the type of players that never use shadow in game (namely for performance reason), then I don't think it would be miss if ya did not included it in ya game.
Its basically dropping the (mod) meshes folder into the data directory, but then again, ya don't have to install the mods. Its just make the shadow match the new body.
The Preparation part in the mod's readme is to create backup of any files before ya add in the mod into the game. If ya do not like the shadow, look into the Un-Installation section and add in back the backup.
Ya must have read the Adding a Custom Shadow to your Beast Race.html. That is a basic tutorial for teaching anyone who wanted to add shadow to any beast race mod.
Unique Shadow Pack 2.0 Read Me.html contains the basic installment and other information.
Correct. Just install the mod like any other mods.
The "construction set" bit (which is more Niftool bit), which is from the Adding a Custom Shadow to your Beast Race.html file, just teach the player how to make their own custom shadow for any race mods (that does not have their own shadow, but would make one for them).