2. Yes, you can.
3. Situational. It's better not to ruin the lord's image—it works both ways. On one hand, showing disrespect to a knight = showing disrespect to the lord, but a brawl over some trifle could also be problematic. In short, you need to consider the lord's character and the customs of the region) But in any case, if it happens without injuries and isn't a systemic problem, it will most likely end with something like "**why on earth did you do that, don't do it again, dammit".
4. If they come running to complain later, it will be handled based on the situation. Generally, a knight is more trusted than some random person, but this can be offset by systemic issues, the presence of witnesses (in case the truth is actually against them), and so on.