But this has to do with with when do you start the clock on a Field Goal after a incomplete pass or play out of bounds under all sets of rules.
You've already received practical answers relating to Field Goals. Allow me to address your other questions; regarding a pass being complete or incomplete; The clock is stopped when a forward pass is SEEN to hit the ground, or when an official signals the pass is incomplete. It's important to understand that along either/both sidelines, especially in the vicinity of the team bench, it can be far more difficult to actually see either, which is why it is so important for game officials in the field to pick up and repeat the wing officials signals whenever possible.
You might consider as well, that although the incomplete pass signal clearly includes the fact that the clock should stop, signals given below the shoulders are far less likely to be seen and adding a "stop the clock" signal, to the "incomplete pass signal, although redundant, can be very helpful in conveying the appropriate message in a timely fashion.
Most officials, relating to a runner's interaction with a sideline, will give a "winding" signal when the run ends, inbounds, close to a sideline and a "stop the clock" signal when the play ends because the runner has breached the sideline. Most, also give a combination of both signals when the run ends, in the field of play, but achieves a 1st down, which would, separately cause the clock to stop.
It's a good idea to consider that the primary recipient of such signals are designed to be the clock operators, and with ANY signal, clarity of the message and the receipt of the intended party, is the objective.