There were several ways to shoot a scene where one person acted as many people. First of all, it could be achieved through post-editing and synthesis. Actors could play different roles and then edit their shots together in the post-production, using special effects to make them appear in the same scene at the same time. Secondly, he could use a stunt double to achieve interaction between the characters. The stunt double could complete the body movements of one of the characters, while the actor himself could play another character. Finally, special shooting techniques, such as shutters and photographic film, could be used to achieve the same actor playing two characters in the same scene. These methods required fine adjustments and processing during filming and post-production to achieve the final effect.
It depends on the context and your interest. Sometimes you might have only one or two things to say, while in other cases you could have many responses.
There's no specific number. It could be just once, or you might go back to it multiple times if it has a lasting impact on you. It all depends on your personal preference and interest.
It really varies. Some 3-act novels might have around 70,000 to 100,000 words, but it can be more or less depending on the genre and the author's style.
In many cases, you can find out. But it varies. Some places make it easy to see, while others might not provide that information directly. You might have to dig a bit to discover if it's available and where to look.
Jidou's appearances in "Guarding Sweetheart" included episode 26 (amusement park), episode 33 (eating ice cream), episode 38 (keys and locks), and episode 51 (Jidou went to the greenhouse to save Yameng). There were more appearances in these episodes. Whether or not there were any fights in other episodes, the current information was not enough to confirm.