uh, one question, how easy is it to make branching storylines in Ren’Py?
That depends on how much you want to happen as a result of a choice.
The documentation should provide the structure for writing out the choice paths, and I also suggest reading up on what are called "persistent flags" - things that can switch on or off at any point in the game and stay that way (there are also "default" variables - they tie to a save file but reset each time you start a new game instead of loading a save).