As others have pointed out, just going for it will give you a lot of great personal and professional experience. You don't need to learn any specific thing to begin freelance work (e.g., learning React first), because any gigs you target will naturally be related to what you already know. Of course, this means you have to be self-aware enough to pick and choose what projects to take on, and which ones to avoid. But even if you did theoretically end up in a scenario where you said to yourself "Crap, I'm not ready, I can't do this," then you'll face it, deal with it, and come out with understandings that make you better prepared the next time around. It's a win-win, really.
Since you mentioned React/Angular, you don't need them to get started on things. But they would be a great asset nonetheless, and probably make it much easier for you to develop single-page websites.