After you've gathered and evaluated your metadata, consider how you might wish to make it available. Deciding on a system for vocabulary management may also have an impact on the data elements you wish to preserve in your vocabulary file. Some open source systems may have more of a standard thesaurus model, making it more difficult to preserve additional information about your vocabulary.
Some additional questions to consider:
Some examples of controlled vocabulary projects for digital libraries at other institutions:
University of North Texas - Controlled Vocabularies, UNT Names
Oregon Digital - Opaquenamespace
University of Houston Libraries Vocabularies - Cedar