For more advice on choosing a supervisor, see your supervisor.
Get on with your literature searching, questionnaire and other methods/vehicle development, and any early fieldwork or you will lose valuable time. However, also be prepared for some changes arising from the formal approval process, so don't become so involved that you can't change some elements.
In length, usually a PhD is around 80,000 words and an MA around 15-25,000 words although this varies internationally. The other answer is that the scope of your work in the PhD or the MA and what it can achieve must be manageable and realistic in the time (MA often one year, PhD 3-8 years) and length available. It is a significant contribution to knowledge and debates but it isn't in theory a mammoth, world challenging activity. Others may change the world as a result of it, but it must be a practicable project.
As you clarify your research questions and your conceptual framework you need to decide which methodology and methods can enable you to ask and (hopefully at least partly) answer your questions. Also pick something manageable and practicable so you know you can analyse the results.
For more advice, see choosing appropriate research methodologies and methods.
Discuss it with your supervisor and hopefully you can find another sample or can restructure your research to still lead to a thesis/dissertation of merit. Sometimes the revelations and problem solving resulting from such problems make the PhD or MA much richer in the end.
You should! Indeed if there are no risks, revelations or discoveries, it could be a little dull. Think how what you find relates to your questions, write about how you handle the decisions you make, discuss developments with your supervisor.
Read it! Reference it and discuss in a dialogue with your own. To ignore it would look ignorant and examiners will expect you to be aware of the developments in the field. It is unlikely to be identical to your work (if it is you might need to re-plan).
Discuss with your supervisor to either ask the university authorities for more time to complete and re-plan realistically the stages towards completion or re-calculate the size and scope of the PhD/MA to make it more manageable in the time available.
Know your whole research and conceptual framework and plan, the decisions made, the boundaries and scope of the work - and rehearse typical questions, handle your stress through managing your breathing, relaxing beforehand, wearing comfortable but smart clothes, arriving early. Know your work really thoroughly and feeling confident that it is important and interesting!
Only 12% of PhDs go through without corrections. Expect corrections, some major perhaps, some minor, some just presentational. It's absolutely normal to have to re-write. This is just a stage. Get in touch with your supervisor and peers who have been through a similar process, identify all the examiners want and fulfill their requirements, and then check it with your supervisor (and peers) and re-submit, showing examiners exactly where you followed their directions (in an attached sheet).
For further information, see Chapter 12 of The Postgraduate Research Handbook by Gina Wisker.