I'm assuming that you're using body-mounted Kadee style couplers.
If the curves are really 24" radius and you're using sectional track (i.e., circular curves that are not "eased"), you may have a problem with excessive coupler swing. Sticking with short 40' cars is probably your best bet. (There's a reason why the 3-rail crowd uses truck-mounted couplers, that in some cases are themselves articulated!)
Throw a few pieces of track together and try a couple of cars to make sure they don't pull each other off the track before you get any further into your layout planning.