How do I know if my PhD proposal is too large / ambitious to be realistically done?

Here are a few signs for you to help you gauge your scope of proposal.

1. Are the topics. you mentioned, present in the future work of the last researcher in that area.
1. Look up the literature of the last two years to find who has done the work?
2. Find their thesis / dissertation online to identify if they have written similar points.
   
2. Look for experts of that area on the web. See what work they are doing. These are easily available on their personal or lab or department websites. I had to go through at least 12 lab websites to know what they were doing. It helped me to benchmark my activity as I knew who were my peers I was working with.
3. Go through #1 and #2 rigorously till you come to a place where you are able to write down at least 2–3 questions that “deserve” solution. My first iteration gave me 8 questions which I , after 3 iterations, brought it down or combined a few to give me 4 questions.
4. Now, identify 3–4 micro areas within the scope of the above mentioned 2–3 questions. These areas are to quantify your work and also act like a safety net. I had 7 areas identified which allowed me to quickly jump ship when my area of study reached a hard wall.
5. After this exercise, show this list and scope of work to your advisor. I should go through in the first attempt and help you define clear goals.
   
   All the best.

Javed GS, PhD