If you've come from an imperative style of programming, you may end up fighting R before figuring out how it works best. It has a beautiful functional style, best demonstrated by tidyverse and map/apply functions. R has the fastest data table / tabular implementation (yes, faster than Julia), which is the standard format for most data and statistical analyses.

1 indexing is standard for numerical languages. The documentation is referenced to papers on the statistical method - I find it usually sufficient, but depends on what package you are talking about.