Good call. The basin road aka Green Gulch is a treat in and of itself. 170 aka the paved river road is one of the best scenic rides around. Big Hill just west of the tepees is so cool that there is a pull off on each side of the summit. If you know the movie "No Country For Old Men" the west pull out view of Colorado Canyon will look quite familiar. 67 from Presidio up to Marfa is a fine ride too. Be sure to explore the old mine town of Shafter along that road. On a different riding day go up Ft. Davis way for the scenic loop, a stop at the observatory, and the old fort itself in town. Check out the Butterfield Stage Museum there too.
If you want a day off the bike we usually have enough water in the river in Sept/Oct to run rafts. There are also several dozen good hikes to choose from. Gee, there is nothin' to do in Big Bend, so why did I move here?
March is slammed. If that is the only time the group ride can go get reservations in now. Many places are pretty near booked up already for next March. This past March I had four days off all month from my guide job.