Most data warehousing initiatives fail (mainly because this level of standardization slows down an agency/company enough that the project gets derailed; boiling the ocean phenomenon).
Avoid building a Data Warehouse right away, but approach it in a slightly different manner.
Build individual data marts instead; each department gets to own its own data mart. These individual data marts would still follow a common standardized technical architecture; and would be able to talk to each other.
For e.g. definitions and metadata in each data mart should follow the same convention.
This paves the way for a final data warehouse – which could simply be a loosely coupled conglomerate of these independent data marts.