I would not use Saltpeter. If you want to use a preservative other than salt use Nitrates. The usage of Saltpeter in charcuterie has largely been made obsolete.
Sodium Nitrate is the compound in found in Saltpeter than gives it it's preservative qualities. So there is no need to use Saltpeter.
That being said Sodium Nitrates although not necessary do add a wonderful smokey flavour and add a wonderful pink hue to your meat. It definitely has some purpose in a brine but yes it is not necessary.
Remember to use at least 8 percent salt solution in your brine. Although I tend to use a 10 percent salt solution to be safe. That means 100 grams of salt for every liter of brine.
Although kosher salts are the norm for charcuterie I have found when brining that a finer salt works better and is easier to dissolve in the liquid.
Don't bother with adding any other spices to the brine. It is unlikely to impart any noticeable flavour.
Brine 3 - 5 days, Smoke and cook very slowly until the meat is tender and delicious.