Javascript API work on Formstack website

I am looking for someone to amend some Javascript code that sits within a Formstack form and which enables an API to retrieve information based on data entered into the form. I am also looking for some fields to be populated from a look-up csv file, specifically when a postcode is entered, the fields are populated based on the postcode of that property. Another API will need to go off and pull in data from a second website and again populate based on a look-up from the form. So it will require connection to two APIs and a set of look up tables.

Also interested in anyone who has experience setting up cloud storage in AWS S3