Well, Derbeder's lists are rather specific and are by no means representative of philosophy as a whole. He is greatly interested in philosophy of mathematics, and this is reflected in his recommendations. Its interesting how preference of philosophical "divisions" reveals much of one's general constitution.
With this connection in mind, I would advise Ptah to seek readings that are near to his fundamental orientation (not to be confused with alignment of "worldview"). Doing so allows one to enter into areas that they would have rejected if exposed to immediately (such as some highly specific and complex work with foreign concerns).
I'll use myself as an example: What got me "into" philosophy was not the academic industry of cute mental exercises (in fact I despise this). It was that charged but supremely careful thinking that thrusts to the "heart of the matter". That which delves into the most uncomfortable areas, stares headlong into the abyss, forces one to give pause and reckon with their existence. Something that addresses what we call "sociology", "history", "logistics", "knowledge" but is neither "history", "social science", "economics", nor "science".
So it is no surprise that my entry to philosophy was through Freud, who is not considered a philosopher at all. Indeed, it was the lack of formality and avoidance of "systems" that drew me in. From there, the doors were open, and I've explored far away from his concerns (including many "analytic" works). However, my essential "searching" craved more penetrating and considered thinking. Again, it is no surprise that I frequently read and "discuss" with Heidegger- In his work, and even personal life to an extent, I find a constitution that is near my own. It is not a matter of alignment of "opinion" but of the essence of thinking.
I've noticed that Ptah seems particularly interested in general "consciousness", so an entry through psychoanalysis and philosophy of mind might be advisable. If you haven't read him already, Freud really is an excellent introduction to the matter and, frankly, essential to understanding how we think of the mind.