Great idea !
What if Napoleon had indeed been another Washington and had retired to be a famous mathematician and physicist between 1803 (the end of the war of the Second Coalition) and 1808 (before the invasion of Iberia)? What effects would this have on world history?
You can have a Napoleon becoming like Voltaire a defender of liberties, sciences and progress : new sort of humanism. With a POD just after the peace and the concordat and with some constitutional changes, a parliament with real power and a military consul who doesn't want to become ruler, you can have a peace inside and outside.
With Tayllerand and Fouche in governement, it will be very interesting inside and outside France.
With no war, you have No nationalism in Europe ! How the monarchies will find support to stay in power ?