Front-end 2018: Technology stack

I recently decided to get into frontend development and chose technologies that I'm interested in. However, I am at a loss about their compatability and use. I can't seem to get a clear picture.

So, technologies I'm interested in: HTML5, CSS3, JavaScript, (obvious, duh) ReactJS

Technologies I'm at a loss about (Don't know whether or not I should use them, how to combine them, etc):

1. Frontend framework (Since I chose a React path, how do I integrate Bootstrap into my projects and do I really need it? If so, what about react-bootstrap?)
2. Block, Element, Modificator (Would it be a good add-on? Are there alternatives? What if I decide to use the next thing on the list, is there a point in combining them?)
3. Pre-processor (Sass\Less)
4. jQuery (Can I combine it with React?)