I have 2+ years or work experience working in salesforce projects. I have worked on apex web services, triggers (on complex logic for handling 3-4 pier level schema), visualforce, apex, configuration work etc.
I think, as per project description, we need to create package, which we can make easily using any data migration tool (comfortable with ANT). And as per 2nd point mentioned, might need to call some external api, which methods we can keep it in some utility class which we would be calling from trigger.
But for clarification please do let me know more details regarding your project requirement or it would be great if could have conversation over this whenever sutiable. Kindly let me know if I can help you in anyway. Thanks.
-Nikhil