Is it an unrealistic goal to want to eventually run a computer with coreboot and a more cybersecurity heavy emphasis?

No, its not unrealistic. However, what I think is unfair to yourself is to attempt this before knowing what you are doing. Think of it like learning to draw. You have good taste, and you see art you like, and want to do it too. Yet your personal skill level, you finger dexterity, isn't yet there to be able to make the art you can visualize in your mind.

If a task is too hard, or to complex, then there must exist a smaller, easier task to accomplish first. Coreboot specifically is an extremely low hardware/firmware level system, but you don't feel confidant in installing a working desktop OS. You have aspirations for cyber security, as well. Find the smaller, and easier task first. Get Debian/Ubuntu working in a VM. Then look at what software is installed, and read about it. If you want to eventually pursue security projects, setup a LAMP stack. If that too hard, just get the A in LAMP. If that's too hard, find out why. What do you know, what do you not know? It's machines all the way down, and its an extremely small chance you are the first person with a problem. Don't worry about "correctness" and focus on the learning experience.

It is 100% achievable, but it is a lot of time. I started with it because I wanted to run a game server for myself. It's a couple of decades later, and I still have a massive amount to learn.