Walking Wounded
Us old warriors who find it difficult walking can bike anywhere.
Paris is a great city to visit. When we went we took the metro and walked everywhere. There are so many sights and I think it really is a city where you have to walk it to experience it.
For bikes, there is velib bike rental (How it works / Paris - Vélib' - vélos en libre-service à Paris - Site Officiel). They have stations everywhere and its very inexpensive. However, we never felt the need for a bike.
For guidebooks, I recommend looking at rick steves guides.
For a three day trip, I'd skip versailles unless it's of particular interest to you. I think it depends on what's important to you. If you are interested in art, you could spend a week or more in all of the museums like the louvre.
Us old warriors who find it difficult walking can bike anywhere.