You need first to decide-----qualitative content analysis of what.
As for a good sample of your topic population, it needs to be representative (effective), and be so with the least number of elements which you can reasonably investigate (efficient).
In qualitative analysis, the sample size does not matter whether it is small or large. What count is that whether the information you needed is sufficiently collected or not? This procedure is called saturation. You will keep collecting data unless you find some new information. The moment you see that new data is not collected, and now information are repeated by new respondents, then you will stop collecting data. This would be your sample size.