Multivariate testing

I'm going to run a test with 4 different variants (3 variants and a control group), and we want to find the variant with the highest conversion.

Are there any resources/methods in R/python to:

• Perform a test to tell if a variant converts significantly better than the others?
• Calculate sample size before performing this test?

Either frequentist or Bayesian methods work for me, thanks! The context is that the amount of data is not huge, I have around 5000 users every month in that funnel.