In terms of eNotes rules, I am permitted to answer only one question at a time so will deal with your reference to motifs in terms of their connection with darkness. The eNotes study guide and navigated pages will help you further your topic and you can post separate questions if necessary.
Darkness features in several scenes in Macbethsome of them most important. Duncan and Banquo's murders take place in the dark; Macbeth's visits to the witches and Lady Macbeth's sleepwalking also take place in darkness.
Macbeth is still not sure whether he should be murdering his king but he sees the dagger calling him towards Duncan's room
and it becomes covered in blood as Macbeth approaches the chamber of the sleeping King. Macbeth’s conscience creates the vision of the dagger.
Macbeth's fear and confusion are emphasized by the fact that it is dark and eerie - he hears voices , "sleep no more / Macbeth doth murder sleep" (II.ii.36) and he has brought the daggers from the room, refusing to return them, anxious to wash the blood from his hands:
"A little water clears us of this deed" (II.ii.67)
is Lady Macbeth's assurance to him. The darkness and the blood having deep figurative meaning and significance. It is the spot of blood "out damned spot!" that will ultimately drive Lady Macbeth mad.
All is never as it seems. Trust is an issue and masking the truth is closely linked to the darkness and the abstract concept of blood:
There’s daggers in men’s smiles; the nea’er in blood, / The nearer bloody.”
"false face must hide what false heart doth know"(1,vii,82).
Ross is alarmed after Duncan's murder and even states that horses ate each other and there were
Other unnatural events ...with the birds and the weather.Is't night's predominance.....darkness does the face of earth entomb/ When living light should kiss it(II.iv.8-10)
Darkness is also capable of hiding many things and changing appearances. In Macbeth, a major theme is the "fair is foul" concept. The witches always appear when there is thunder - in itself creating dark shadows and a foreboding. In Act IV they are in a dark cave when Macbeth visits them.
Macbeth's "vaulting ambition" is so strong that he realizes that he must halt Banquo's bloodline - as in heredity as his son's will succeed Macbeth - for whom he apparently killed "fair" Duncan. That is unacceptable. The darkness in Macbeth's heart is cemented as he goes from one murder to another.