Hi ab...
3. This is commonly called acceleration, which is the rate that your speed changes. If your acceleration is zero, your speed never changes; and your speed changes faster with higher acceleration. The thrusters add acceleration according to f=ma (add more thrusters, get higher acceleration) but I did not see a sensor that would tell you the overall acceleration (linear or angular) for the construct as a whole.
4a. I mean an input path that either adds to or subtracts from the input value.
4b. (Meant to write 5) a way to combine multiple output values to combine with one input value.