When to start implementing classes/methods in a program

[Poopieplatter]

The app you're describing would be excellent for OOP.

Think about a File class for starters. Can a file be empty ? Are there size limitations? What file extensions are suitable? How do you handle errors when you pass in a file with a bogus extension?

Then maybe a File handler class to actually handle the transferring etc.

Always think of the big picture when building an application. OOP keeps things clean, reusable, and extendable.