I lived in Paris for a year, am so jealous as it's a fab city.
You've had great advice already, and I can't help with hotels as didn't really stay in any.
My 'insider' tips would be:
- Go to Chartier Restaurant (Metro Bonne Nouvelle) - very French, quite cheap and fabulous
- Walk wherever you can as Paris is pretty small (I walked across the whole city from Nation in the East to CDG Etoile in the West in 2 hours). Some metro stops are literally 2 mins walk from each other
- Walk from CDG Etoile (Arc de Triomphe) down the Champs Elysees, across Place de Concorde and through the Tuileries to the Louvre. It's a fab route that takes in loads of good sights (and shops!)
- There's a fab spot to stop and chill in the Tuileries by one of the big ponds - you can see the Eiffel Tower AND the Arc de Triomphe
- Go up to the roof terrace of the Samaritaine department store as they have a viewing platform and you can see all the best bits for free
- Another great walk is from St Michel down to the Jardin de Luxembourg, out the other side and then down Boulevard St Germain - there are two amazing cafes at the end (Deux Magots and Cafe de Flore) where Sartre and Simone de Beauvoir used to hang out. Great for coffee and people watching
That's all I can remember for now, but whatever you do you'll have a fab time I'm sure.