I am trying to create a batch but it's telling me that class 23 does not exist?
Is there something I should be completing in SPRO first?
Also I am trying to extend my material by adding a classification view, would I need to make new material and start from scratch that way?
23 or rather 023 is not a class. It is a class type to classify batches. A class of that type needs to be assigned in the material master record, "Classification" view, then batches of this material will be automatically classified within this class.
If you want to add a classification view for an existing material, just go to MM01, enter the material number and create the view. You don't need to create a brand new material from scratch. You just need to create the classification view in MM01.