Contact upsert form -- Referral program

We'd like someone to help us utilize Salesforce API to create a form within a microsite that would intake a contact ID (passed through URL encoding via email), verify the users' email address, then allow that user to input up to 5 emails that we can then insert as new leads in our system. Few requirements: * Our design team can create the design, assets, and basic framework for the microsite -- we just need help with calling the right Salesforce information & verifying * Since we are going to email our database of users, with the email attached to their SFDC contact, there shouldn't be a need to insert a contact intially. In fact, I'd prefer it not insert and just give an error instead. * We don't utilize the SFDC Lead Object right now and just pass everything to Contact/Account -- that may change in the future but this will need to happen before those possible changes. Willing to negotiate budget/ongoing work. Awesome company and fun team to work with :) located in NYC; a developer in the NYC area preferred but not required!