Hi,
I might be able to help a bit with this. I lived a small time in the south of Paris in Igny, which is on your route (now I live south of Amiens). Also, when I cycled to Barcelona I went through Oréans. The main problem you might have is that Paris isn't easy on a bike (unless you're in the centre, which is great). I think the nicest way to do it would be to go from Dourdan, Saint Remy le Chevreuse, Jouy en Josas, Buc, Versailles. Don't go anywhere near Trappes or Plaisir - Trappes in Particular is a bit dodgy and far from pleasant. The area I've indicated takes you through the Chevreuse - which is really nice. Once you're in Versaille, I can't really comment as I haven't ever attempted to cycle from Versaille into Paris before - but it looks like the road through the Forêt de Fausses Reposes would be quite nice. As for Orléans, I really liked this town. It's cycling friendly and the centre is lovely. I took the N20 from Dorlans. It's not a road I particulary recommend - it's quite busy and the scenary is boring. You could go through the Gâtinais Français, which is really nice, but it does add a few kms (actually a lot of kms) to your trip.