Hi Ian.
To be honest there’s only one Welsh, but various dialects. None of them are the official one. So it’s a bit like the English dialects without the Chelsea one. Except that all are honoured slightly more than the English dialects. You only need one - I’d go for “Northern” if you visit Wrexham.
There is a literary (written) dialect which is used in varying degrees of formality in documents and older books. However, no-one actually speaks like that except when reading from the documents, so it’s enough just to know that it exists.