"Does the order only work within the Type and they always trigger 1:1 types first?"
Correct. The transformation rules sequential process the Types and then the order within each type. 1:1 mappings will always come before Composite.
Based on the information you provided it sounds like you could put your Expense+Department mapping as the Composite Rule and then put a Mask for everything else; from * to None. This way the expense account mappings get picked up first and everything else will fall to the mask rule.
Lastly, if I understand your PS correctly, I would strongly encourage you to avoid making transformations in the Data Source steps. Rather, make these changes in the Transformation Rule itself. There are certainly times where it makes sense to transform the data during sourcing, but you'll have better auditability and maintenance if you put those transformations in the Transformation Rules.
Hope this helps and follow-ups are welcomed. Cheers! -db
