Hi Bose,
You could use SAP Best Practices as a reference for WT tax codes depending on your Country.
In my case I mostly used alpha numeric for WT Tax Type (name it similar to the tax concept) and numeric for WT Tax Code with rates or WT concept in the description.
Also consider it should be scalable. In one customer they wanted to use 1 WT Tax Code per WT Tax Type. As WT Rates changed continuosly, WT Tax Types also changed continuosly and grew up exponentially.
Kind Regards
