Rav Nahman did not hold of learning philosophy at all even, -- of the great sages of Israel,  To some degree that make sense. But utter ignorance leaves one to prey of the many glittering ideas out there that with the most cursory examination fall to pieces. You need  sense to know what to learn.

  My suggestion is Plato, Aristotle, Plotinus, Kant, Leonard Nelson [a Jew that started a new sort of approach to Kant.]

[rav nahman was right about everything else. in particular he said not to learn the guide of the rambam and i can  see his point.

what is more I would like to recommend the two treaties of government by john locke