We have a developer at our company that needs to get set up so we can integrate an external homegrown system with a custom object in our Salesforce.com instance.  I'm trying to understand what do I need to set up so this developer can develop and test REST API calls to pass data to and from that object in our SFDC instance.  We have Enterprise Edition.  I set up a Developers Sandbox on our SFDC instance.

Here are my specific questions:

1. When I set up his User Profile in our SFDC instance, are there any special permissions that I need to give him access to to be able to develop using the REST API?  Are there any particular settings in his profile that must be set?
2. Does he still need create a Force.com account to be able to develop against the developer sandbox associated with our SFDC instance?
3. Is there anything else that I need to give him access to?

I apologize about asking this Getting Started question, but I read through many Getting Started posts in the community and the Getting Started section on Force.com and I couldn't find the answers to these questions.  Thanks in advance for any advice.