Carl Scheuer No, everything else is an option. While I would recommend using Encapsulated Citric Acid (it adds tang and is a cure accelerator) and Sure Gel as a binder you are fine with just the cure and the seasoning. Some people like making a Summer Sausage with no tang and if holding it overnight before smoking isnt a problem for you then you are fine there, and just make sure you get really really good protein extraction.
If you have issues, or want a different result then try those additives next time! Good luck, and please post pics if they come out really well!