I can't find a good source of info for RSCA, but I think it's a combination of angle, movement, and impact that triggers it. Even if RSCA is "off" the side airbags might still trigger in some situations, but it's less likely. With it "on"/normal it's still unlikely that you will unintentionally trigger the airbags off road.
There's a lot of hate for VSC on here, but it really can be useful on slippery roads and snow. If you want to have fun and do donuts or spin the tires it gets in the way, and there are some situations where it might cause difficulty, but in general it is trying to help and make up for the average driver's lack of skill.
The main function of VSC is to try to keep the vehicle going in the direction the driver intends. It senses the rate of rotation of the vehicle and compares that to the steering wheel angle. If they don't match, it brakes individual wheels to try to correct. It can do this better than a driver in most situations because you don't have a calibrated gyro to sense rotation or four feet to brake each wheel the correct amount.
It also tries to help you maintain traction and keep from spinning the wheels. This is sometimes called TRAC or traction control, but it's the same system that controls that, VSC, ABS, DAC, HAC, ATRAC*, Crawl control* (*some models), Smart Stop, EBD, brake assist, Auto LSD (2WD models), etc. Slipping tires have much less traction than ones in good contact with the ground, so traction control tries to keep you from doing that. It does so by braking wheels that are spinning too fast so the differential sends power to the wheels with traction, and by reducing engine power so you don't overpower the system. It's helpful to get you going if you are off road (or on a slippery road) and one or more tires don't have traction, but it's not as good as a locking differential.
