Plans - where to go, and when?

Cycling in Europe has been a goal of mine ever since I started watching the Giro d'Italia and Le Tour from a young age.

I now have the option of doing just that, and am wondering on just where to start - departing from London, do I train/ferry to Calais/Rotterdam and just go from there?

Which way do I go? Which countries and cities to see?

Can I wild camp?

Spring seems like a logical time to start this, the last of the snow is melting and the sun is starting to thaw western Europe.