Salesforce project

I am looking for a technical solution to implement a function that converts numbers to "letters". The goal is to be able to call this function from any object that has a field of type Number. For example, for an opportunity that amounts to $150, the function should return "One hundred and fifty dollars." How will admins be able to consume your feature? I need the technical details of the best solution, the best option, whether by Apex, Workflow... or by Flow, and some pseudocode, I don't need the coding, but I do need a little detailed analysis of this. And on the other hand: To import a "Campaign" with "Campaign Members", into Salesforce. We agree to provide the list of "Leads/Contacts", from Salesforce, to be included in the Campaign object. What columns would we expect to see in the Excel sheet that we need to load? I need the explanation of all the necessary steps to upload all the members of the "Campaign" in the Campaign object, to the correct campaign.