Brining a PB doesn't help a lot. Because of the size, you'd have to brine it a day or even two for it to penetrate very far.
My suggest for a first time is no brine, no injection, just a rub and smoke. Start with that build a baseline of how it works then start experimenting with various options. If you brine the first time you won't know if it's the brine or something else when it comes out good.