OP wants to "develop a personal philosophy." So they will want to learn the state of the art of philosophy. Starting with Plato to learn philosophy is like starting with Archimedes to learn physics. They would be much better off getting a lay of the land from a modern writer. In fact, just as you don't read original research papers to learn physics, I wouldn't recommend OP even read the primary works of any influential philosophers until they've gotten an overview of philosophical thought writ large, a general outline of the specific philosopher's thinking and how it changed over time, and how the philosopher's thinking influenced others. Wikipedia would be a great place to start.
There is simply too much philosophy for any lay person to read thoughtfully in their spare time. And philosophy isn't like math or science, where a small kernel of knowledge and consensus among scholars slowly grew over time. It's more like sculptors shaping clay into pots. Subsequent sculptors may immitate past artists in certain ways, and certain long term trends may emerge, but there is a distinct lack of consensus on almost everything in philosophy.
In my opinion, the reason for this is that philosophy as a means of understanding ourselves and our world beyond what science can tell us is essentially futile. In Plato's time, there was no delineation between science, philosophy and mathematics. The word "philosophy" meant "love of wisdom" in Greek. A philosopher was just someone who wanted to discover knowledge of any kind. Over time, philosophers systematized certain areas of knowledge, giving us math, logic, and science. The areas of knowledge that we were able to systematize are no longer considered to be philosophy. Philosophy today, almost by definition, is the study of problems that have resisted all attempts at systematic understanding for two thousand years. It has no wisdom for us. If you want wisdom, look to math and science.