The challenges in FCC are there to show you some tools to complete some specific use-cases. The projects are there as the actual tests of your skills and knowledge.
If you want to see what you really need, skip all the challenges and start a project and see what it takes. Don’t expect to instantly finish the project, or even know where to start, projects are the closest you can get to a real development project with all the freedom and challenges you would normally run into with the average project.
If you completed everything you can say you have experience with full stack web development, along with experience with things like data-science.
The best way to practice is to go out and build your own side-projects with the skills you have so far, so if you have a portfolio you can build more static web pages. Id say once you learn Jquery you can build something more complex, but you will start to see the “limits” of JQuery based sites.
Don’t limit your learning to just FCC, side projects are great times to expand what you learn to include new things.
Once you learn React, and a good amount of JS you can probably build almost anything complex. (With help of external sources for React/JS).
Throw in the nodejs+database sections and at that point you can build the average full-stack JS app using the MERN stack.
Your always welcome to apply to jobs at any time, you might get lucky and get a job with 0 to no experience, or get rejected. The key is to learn why your rejected for a job, so you can go out and improve your skills that you are lacking. If its just simple experience, find out what experience you can and go seek out ways to get that experience.
I think FCC teaches a good amount of topics, but depending on the job you probably would want to focus on other materials, or more experience with what FCC teaches. For example, if your applying to a job where they use VueJS, your React skills kind of carry over, but VueJS might be a better bet if most jobs in your area ask for that. (This is just an example)
Goodluck, keep learning