2. If the death of the tooth nerve has any influence on the teeth, then he will not feel pain and the teeth will indeed become brittle.
3, as for whether the tooth nerve will feel cold or hot after it is gone, it is sheer nonsense. The pulp can only feel pain, but it can't feel cold or hot. As for what it usually feels; Hot and cold are felt around the teeth, not the pulp.
4, orthodontics or porcelain depends on the tooth. If your tooth is long and crooked, you can do orthodontics (of course, the possibility of tooth extraction correction is not ruled out), but if the tooth is color or rotten and moth-eaten, it is useless for you to do orthodontics, which is generally porcelain restoration.
From my experience as a dentist for such a long time, if your teeth are good and there is nothing bad at all, try to keep them. After all, every tooth of yours is unique, and it's ok to look ugly. Is it mainly practical or the most important?