Sampling Twitter Accounts


I need to do a content analysis of certain types of Twitter accounts. There are in total 19 of them (N = 19) but I need to take a sample due to resource constraints.
I want to have 95% confidence (Z = 1.96) and a margin of error of 5% (E = 0.05). In order to understand the variability of my population, I calculated the standard deviation of all tweet frequencies from the 19 accounts which turned out to be 0.63 tweets/day.

The population proportion (p) should be 100% because every single account is of interest in my study. However, online sample size calculators tell me that my sample size is 0 when I enter a 100% population proportion.

Basically, I am not sure which formula or approach is appropriate to calculate my needed sample size.

Any kind of help would mean a lot to me!