What are your research questions? To what extent can you test them? How would you justify the viability of your questions?
What are your hypotheses? How would you test them?
Why would this design be the most appropriate for answering the research questions? Conversely, why would qualitative and mixed methods designs not be appropriate?
What quantitative approach would you select for this study? Why is that approach the most appropriate one for answering the research questions?
What theoretical framework or perspective would you use?
What is your target population? How would you identify and recruit participants?
What factors would contribute to determining appropriate sample size? You will not need to calculate sample size for this assignment.
What are the independent and dependent variables?
If appropriate for your plan, what instruments might you need?
What data collection procedures might you use?
Why would those be the most appropriate methods to use? How would that data help to answer your research question(s)/hypotheses?
What are threats to validity? How might you mitigate them?
How might you analyze the data?
What are the ethical considerations related to the plan?