A good place to start would be 'Die Fragmente der Vorsokratiker' (The Fragments of the Pre-Socratics) by Hermann Diels (1903). This book would probably answer all your questions. Unfortunately, it's never been translated into English. The good news is we have the next best thing - 2 books by Kathleen Freeman:
1) 'The Pre-Socratic Philosophers; A Companion to Diels, Fragmente der Vorsokratiker' (1946)
2) 'Ancilla to the pre-Socratic philosophers: a complete translation of the fragments in Diels, Fragmente der Vorsokratiker' (1948)
1) is available on archive.org. If you have an hour or so to spare, read through pages 285-326. The amount of information, heavily supported by testimonia and actual fragments, is all you can wish for and then some more. The arrangement by subject-matter is also helpful to quickly see similarities and differences between Democritus and Epicurus.
2) is not available on archive.org but it's digitally available at 'sacred-texts' website (link below). The link will take you to the ancilla containing fragments of plethora of Pre-Socratics. It's the only place online I'm aware of where all Democritus' fragments are available in English.