Hi there, I am new to Salesforce and trying to get started with REST Api's for things like
- getting Auth'd
- creating Leads
- converting Leads to Opportunities
- updating dollar amounts, etc

Been jumping through screens and docs and have a few questions.

I read somewhere it must be a Developer Edition account to use Api's. How do we determine what type of Organization the account is in? 

Somewhere mentioned Api Enabled must be turned on. Where do I go to enable/disable Api services needed?

Is there a list of Api services with documentation? Trying to find out how to navigate to Api's and their docs. Is Data.com part of Force.com.

There are 4 types of Sandboxes but not sure which to try Api's with. Can the Developer Sandbox be used with Apis for Auth, Lead gen, Lead to Opportunity conversion, etc, or is it limited to only certain Sandbox types?

All help is appreciated, thanks!