It's well written, but lengthy, I think. In my view, I think the three primary, but related differences are that:

a) Existentialism deconstructs meaning through critical questions; Buddhism deconstructs meaning through non-judgment.

b) Existentialism argues that constructions of meaning are individual; Buddhism argues meanings are universal, but a matter of experience, not principles or rules.

In practice then, existentialists are free to construct whatever meaning they individually please. An existentialist thus can be evil and destroy everything simply because of his individual opinion or desire, and even rightly call it "good". The convenience of this perspective is that it seems to be exactly what everyone does anyway. The funny thing is that people would rather accuse and defend from hypocrisy than just accept this as a fundamental, which is of course one of Nietzsche's favorite devices.

A Buddhist rather often seems to seek some universal, more general goodness, connection, peace, or calm.

I think the postmodern connections are a stretch. An inherent subjectivity to meaning does not favor either existentialism or Buddhism, I think.

As an aside, one quaint comparison I've noticed is that Buddhism promotes "mindfulness" whereas Camus promotes "mindlessness". Sometimes I think the terms would be more accurate if they were reversed.