I am commenting in Amy's place on this thread. We have day hiked or backpacked in Coe over 260 times and have covered every bit of the place at one time or another know the park quite well Given 7-9 days at 12-16 mpd yields a range of 84 to 144 miles, which is a significant variable in planning a trip. One of the really nice things about Coe is the density of walkable old ranch roads and trails. Thus, a person could plan a trip at the extreme end of possible mileage and, if necessary, easily cut off a portion of the trip if daily mileages are not met. Just carry a copy of the excellant park map and you can adjust your plan as you go along. The map includes trail mileages between trail junctions so it is simple to figure out how far it is from one point to the next.
If I had a week available, I might walk a perimeter route around as much of the park as possible, taking in Red Creek and the Orestimba, Mustang and Burra Burra Peaks. Or I would head for the far northeastern portion of the park which is distant from the road based entry points and is seldom visited. Head out Red Creek to Upper San Antonio Valley; walk the Mt. Stakes Trail and Pinto Creek; camp at Paradise Flat for a night; climb Robinson Mountain. Or, if you are willing to do some thrashing, go up rarely visited Snod, Grass, and/or Cone. All of these places are rarely visited and you should be able to expect solitude.
Best of luck,