I am trying to start a react native project using the React Native CLI method (https://reactnative.dev/docs/environment-setup). My first question is, if I have a mac and my friend has a windows computer can we both work on the same app? Also, how do I configure one single code base for both ios and android? Do I just follow the installation instructions for both in a single project? Thanks!
Yes, you can work separately on windows and mac for the same app and you don't have to configure any kind of codebase as react native is hybrid app development technology, you just have to write a single code for both the android and ios platforms. To install react native CLI just follow the official document on your specific platforms because both of them have a slight difference in the installation process, after successful installation, I would suggest you to use some kind of VCS(Version controlling system) like git or svn.
I am also working in the same process as you have described I am developing in windows and my friend is working on the mac.
feel free to contact me I will help you if you have any kind of queries