Fuel should be fine for at least 100 laps or so, think in perspective to how far they could go at Martinsville, and then add about 10%.  I think it is because there is so many unknowns they don't want a 100 lap dash or something like that.  The event is going to take most of the day (Q, heats, LCQ), and then a 100 lap dash could take 40 minutes including 5 cautions (Just looked up some WoOLMS).  Most features are 35, 50, 75, and (less often) 100 lap races.  NASCAR doesn't want a main race to last less than one hour, as they want to put on a "show" like normal.
What I don't understand, is will they reward efforts in the first two segments?  Or will the last segment be the only one to matter?