there is no official limit to design, just your desires/abilities. no, you probably wont find a crossover at a ROAR nationals IFMAR worlds, but many local tracks do have them. it usually consists of one direction jumping over another. look on youtube for track designs. there are also jumps refered to as "singles", "doubles" and "triples". what that means is there are several jumps of the same dimensions in a row and the numerical designation is how many can be jumped at a time. using the first as the take-off point, a single is when the rc lands on the second jump, a double is completely clearing the second and landing on the 3rd and a triple is jumping over the second and third and landing on the fourth.

some tracks also have what are called chicanes. pretty much an abrupt swerve. dont forget about elevation changes. they can take a rather dull track design and transform it into one of the most entertaining tracks ever made.this can be achieved by simply building the track on a hill side or if you dont have any, just dig out part of the track and pile the dirt elsewhere on the track.

just a thought, if you were to extend the length to 150' and build a straight almost as long, you would have a 1/10 scale quarter mile with run-off. the strip would be 132' and a wide banked corner would give sufficient distance for slowing down. when not using it as a strip you could place turn barriers to follow the actual track or build plywood jumps for something like a high-jump competition or for actual racing.