Well, you dont need to understand back end at all to learn React, JS knowledge is whats useful, but even then you dont need adv JS knowledge… basic JS, ES6 and HTML is plenty enough for a smooth transition into React.
Personally I dont see anything wrong with learning React and Node at the same time…I pretty much did. I did not feel confident with React at all…had only done this course and a super basic React SPA mockup when I decided to do a full stack React app course. I learned quite a bit and glad I did it…but I dont know…I guess just go for it and if you find it getting overwhelming or frustrating, then scale back and concentrate on one thing before moving on to the other.