Specifically sources about Octavian, when he was young, before the civil war and before or during his initial rise to power, as opposed to him as the first emperor.
I can't answer all of this but a good starting point would be Suetonius' Twelve Caesars - Julius and Octavian are the first two covered and although he was writing at least 100 years later, Suetonius covers a lot of their lives.
There's also the Res Gestae Divi Augusti, which was basically a huge wall Augustus had built before his death. On it, he inscribed his life story and it was a huge propaganda tool listing every title he ever held along with a lot of other stuff 🙂