Merging and Calculated Columns in Power Query vs Calculated Columns

Star schema is the prefered approach for tabular models (i.e. DAX, so tables with relationships). That said I would recommend doing as much of the data preparation as possible in PowerQuery (with the cost of the model refresh being slightly longer), and avoid calculated columns at all (they come with a cost of using additional memory, and are not really necessary for the row level calculations - that's what the iterator functions like SUMX are for https://dax.guide/sumx/)

A very good article describing the differences in more detail:
https://www.sqlbi.com/articles/comparing-dax-calculated-columns-with-power-query-computed-columns/