What role do you want references to play in making your decision?

Seeking references from others tends to be a slippery slope because every company's situation is unique, and therefore no two people's report will be the same. Also, be respectful of the fact that any firm which does the quality of work you seek will typically have a highly confidential relationship with its clients, and client names will likely be given out sparingly, just as you would expect of that firm in relationship to you. While it is certainly advisable to speak with one or more parties who can attest to the quality of a provider's work before you hire them, generally this should be one of the last steps in making your decision. The first step is to scrutinize closely the firm's fit for you, as per questions 1-6 above. When you are convinced that you have found the right match for your organization, then ask for the names of one or two people who can affirm that you have made an appropriate decision.