I take an approach that values lineage
1. Lives and opinions of eminent philosophers - Diogenes Laertius
Theres good biographies on Thales, Anaximander, Anaximenes, Democritus, Anaxagoras, Pythagoras, Heraclitus, etc
2. Pythagorean Library and Sourcebook
3. Nichomachus on Arithmetic and Harmonics
4. Mathematics Useful for Understanding Plato - Theon of Symrna
Read Plato, he combines heraclitus, socrates, and pythagoras according to diogenes
5. Euclid's Geometry and Optics
6. Lucretius - On The Nature of Things
7. Aristotle, the physics then Simplicious's then Philoponus commentaries
8. Sacred Geometry For Artists, Dreamers, and Philosophers by John Lieben
This is my intro thus far and what im currently doing when im done ill update it
Updated