Glad to have you IFancya! It sounds like you have made a lot of progress already.
Because you seem oriented toward the details, rather than the Emily Austin book I would recommend your going straight to the DeWitt book as the most meaty and sweeping of the two.
I would not worry about the Epicurea as it is more of a "glossary" and though it is organized by topic, it is not presented in a way to facilitate progressive understanding. It's more a reference for those who know what they are looking for to find supportive citations.
I'd also recommend anything by David Sedley, especially the Epicurus section of Long and Sedley's "The Hellenistic Philosophers."
I've also prepared a FAQ answer on that if you haven't seen it - let me find it.
Looks like the most recent update to the reading recommendation is at this link: