So, the research question at hand is: Of farmers growing a biofortified corn variety, what percentage of their total corn consumption is biofortified?

I am currently trying to calculate the sample size needed to answer the aforementioned question.

It seems as though the sample size equation for an interval estimate of population proportion should be sufficient for the question at hand (reference: https://select-statistics.co.uk/calc...on-proportion/)
*With a total population of 4,000, 5% margin of error, 95% confidence, and an estimated population proportion of 50%, I'm getting a total sample size of 351

However, given that I trust Stata much more than some random online calculator, I tried computing this directly in Stata and can't seem to identify the correct sample size test. I attempted using the command:
power oneproportion
But this requires that I know something about the hypothesized and alternate proportions, and since the null proportion can't be equal to the alternative I'm not sure what to do.

So my question for you stata and statistics experts is two fold:
1. What is the command in stata to calculate the sample size for a population proportion?
2. Given the limited information I've provided, is this the sample size methodology you would be employing? *bearing in mind that literature on this topic is rather sparse

Thank you very much for your assistance