You, my friend, are suffering from Procrastination.
You have the idea - but you're putting SO MANY barriers in front of implementing that idea. You're finding excuses NOT to just sit down and write code. You're procrastinating.
I know this because I too am guilty of it - been guilty of it all this week in fact. I have an application to write for a business client - it's Wednesday already and I'm still "thinking over it". I should get started on it, preferably before this week is over.
Listen. Forget TDD. Especially if you're a team of 1. Just sit down, decide on an IDE - vim will do, even! - and start writing Code That Does Something for your idea. Got stuck? Google for "how do I <do this in $language>?", see how to do it, then write the Code That Does Something.
"But, the TESTS!" - here's my method of development (as I'm on a team of 1) : A) Write the Code That Does Something. B) Run it and see if it Does What You Wanted It To Do. If it does, great, carry on. If not, sort that bit out until it does. Then carry on.
Oh and stop procrastinating.