i would recommend Lama Zopa Rinpoche's '' how to practice Dharma - teaching on the eight worldly dharmas '' this is not a kagyu book as you know but i think it is a very important and one of a kind work on buddhist psychology and the core of buddhist mind training practice, even though its not lojong.
i would cover this buddhist psychology and mind training aspect of mahayana before introducing vajrayana.
the other book would maybe be sun of wisdom by khenpo tsultrim gyamtso. some middle way text.
If the thought of demons
Never rises in your mind,
You need not fear the demon hosts around you.
It is most important to tame your mind within....
In so far as the Ultimate, or the true nature of being is concerned,
there are neither buddhas or demons.
He who frees himself from fear and hope, evil and virtue,
will realize the insubstantial and groundless nature of confusion.
Samsara will then appear as the mahamudra itself….