Why we must have a confident mind?
What is a confident mind according to the Lord Buddha?


From your quote, confidence is translated from the pali word pasannacitta. Pasannacitta literally means devoted mind, and can be interpreted as a person having faith (saddha).

https://www.wisdomlib.org/definition/pasannacitta


  Why we must have a confident mind?


It is considered one of the five mental faculties/indryas that aids progression towards enlightenment.

https://www.accesstoinsight.org/tipitaka/sn/sn48/sn48.010.than.html


  What are the differences between confident and conceit


Conceit (mana), is a cetasika with attachment/lobha as base. Mana means that we are attached to the misconception that there is a self that is superior to others.


  What are the differences between confident and clinging to a view


Primarily the difference is the fruit of their karma. Besides being a mental faculty mentioned above, AN 5.38 also lists five benefits of saddha for laypersons, for instance.

https://www.accesstoinsight.org/tipitaka/an/an05/an05.038.than.html

Clinging to a view, on the other hand is simply not beneficial, and perpetuates dissatisfaction. Your comparison with conceit seems like an appropriate example.