Sample Size Estimation for Observational Study

I'm conducting a medical research project that involves an observational study. I need assistance in estimating the appropriate sample size to ensure the results are realistic and true.

The specifics of project 1 are as follows:
- Data Type: Qualitative data
- Study Nature: Observational study
- Variables: Planning to observe 3-5 variables

The specifics of project 2 are as follows:
- Data Type: Qualitative data
- Study Nature: Observational study
- Variables: Planning to observe 1 variables


Ideal skills and experience for the job include:
- Strong background in medical research
- Proficiency in qualitative data analysis
- Experience with observational studies
- Expertise in sample size estimation
- Excellent understanding of variable analysis

I am looking for someone who can provide me with a valid estimation of the sample size necessary for my study to yield true and realistic results.