I have done entire C and O a few times with friends. My wife wanted to try it for the first time together. We decided we would not have time to do all 184.5 miles so we did almost 80 miles (Williamsport to Whites Ferry)in three days. It was a great trip. We wanted to do it without help from others so the logistics took some careful planning. Here is the itinerary in case you want to try it:
Day 1 - Drive to W.port and check into Red Roof. Leave bikes/gear in hotel room. Drive to enterprise car rental in Hagerstown (its very close to W. port). We both drive to Whites Ferry and leave our car there. Both of us now in rental go to Brunswick family campground and drop off camping gear, clean clothes and food inside a large plastic tub. I contacted the person who runs the campground and she said no problem leaving stuff until we get there two nights later. Drive rental car back to W.port hotel.
Day 2 - In the morning drive rental to enterprise and its their policy to give free rides home so they drive us back to hotel. Pack up bikes and hit the towpath. Ride to Shepherdstown and spend the night at Quality Inn.
Day 3 - Leave S.town and Ride to Brunswick family campground (camping stuff is there waiting for us). It was nice not having to carry tent, sleeping bags, etc. on bike).
Day 4. Leave campground for Whites Ferry where car is parked. Get in car and drive to Brunswick to pick up camping gear. Head back home.

We are very slow riders and stop to look around every lock, lockhouse, cave, etc. Also spent time in downtown W.port and S.town. Looked around Harper's Ferry and Ferry Hill Plantation for a while. We fished and swam in Potomac a few spots.
Great three days on the towpath.

Correction - Meant to title this discussion Williamsport to White's Ferry (not Cumberland).