A big question is how much do you like your warranty? Cuz the minute you start down this path you can kiss it bye bye.
You've got a great place to start with this build up
I'd recommend getting at least 5K on the clock before touching the system to let it As I said before, you should upgrade your fuel delivery before you upgrade your turbo, diesels work well running rich, but not so good lean, you just have to be very careful with your DPF on the 6.7Ls. If you live somewhere that you can delete it, then it's the best way to go as it removes that complication all together. If you can delete it, then look at the H&S performance BlackMAXX for a tuner
Are you looking to use the stock turbo as your high boost or your low boost in your compound system? and would you consider a larger single turbo rather than a compund system? like a 78mm? The garret 78mm can boost up to 60psi on it's own, there's just a bit of lag to get to full spool up.