Need help with a simple typing game

Hi all,

Just had my cousin over (8th years) and she wants to learn to type blind. As I need to refresh my flash skills (just bought flash 8 skipped on flash mx 2004). I thought it would be a fun project to create a simple typing course and a simple typing game for her.

I want to start with a simple typing game, as I must find my old learn-to-type book.

For the game:
1 What I had in mind was just some random words scrolling from left to right.
2 Each letter disappears on the right stroke
3 Level is based on the scrolling speed
4 You get 5 healths
5 Level over when it reaches a certain point on the right side
6 Game Over as you have no more healths left.
7 Must do something with a score system

Misc.
UI elements graphics

How would a professional like you structure this game on paper and what would a structured way be to develop this simple game???

Like to reuse the typing part of the game for future games (like falling letters)

Where to start
Tx in advance