NCERT books, previous year's question papers, and sample papers are indeed the most imperative while dealing with boards. However, they alone should not be your guide.

While most questions may happen to be asked from NCERT textbooks and previous years' trends, do not forget that board exams tend to change their pattern after a certain period and new questions may appear.
A holistic approach would involve studying and practicing the following:

Concept Understanding

Concentrate on the concept and not just on the formulae and facts.
Read NCERT textbooks and reference books for details.
Multiple Choice Question Practice
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Solve a vast number of questions from various sources such as NCERT books, previous year's papers, and sample papers.
Practice numerical problems as well as theoretical questions.
Time Management:
Practice answering questions in a set time to improve response speed and accuracy.
Attempt Mock Tests.
Regularly revise the topics and strengthen your concepts.
Make short notes and flashcards to help you revise more quickly.
Ask Clarification
Don't be afraid to ask your teachers or classmates if you have doubts
Join study groups to discuss concepts and solve problems together.
By following these guidelines and combining the resources of NCERT textbooks, PYQs, and sample papers, you can really prepare for your board exams and achieve the desired result.

Yes, this would be enough if you have good understanding of concepts. Question do not come directly from sample papers or previous year question papers but the pattern and type of questions is very similar. If you have studied NCERT thoroughly with understanding of subjects rather than just rote learning,then you can surely score good marks.

Sample paper and previous year question papers will help you analyse your preparation and your understanding of concepts. You can analyse your strong and weak topics and accordingly you can revisit to books to improve your concepts. Solving previous year papers will also help you with time management in exam.

Yes, studying NCERT textbooks helps you in getting direct questions from the book in the board exams, previous year question papers (PYQs) helps you understand the exam pattern, question types, and difficulty level, allowing you to prepare accordingly.

While sample papers is generally considered high level preparation it provide additional practice with different question formats and help you assess your preparation level high.

as the majority of questions asked will be based on the content covered within these resources most questions will indeed come from these sources.

Have a great day ahead!!