I have to disagree with a lot of the posts out here on this subject so far. Yes, general relativity is about the physics, but as a physics grad student, I've had some of my greatest frustrations just trying to "learn the math through the physics". I think that it's very helpful (at least it has been to me) to learn the math on it's own from mathematics text and then, once the math is understood, pick up a physics text so you can focus solely on the physics ideas. Again, this is all my own humble opinion, but it is what has worked for me, and many of my friends in the field have related similar stories.

To answer your question more specifically, here is what I would recommend:

On the math side:
1) Review single variable calculus
2) Multivariable calculus
3) Linear Algebra (check out Axler's "Linear Algebra Done Right" - this book is amazing)
4) Differential Equations
5) Differential Geomotery

General relativity is all differential geometery, so understanding this is what you're shooting for. However, just knowing the math isn't enough; you'll need to get up to speed on physics as well. So, assuming you've had an introduction to physics somewhere (high school or undergrad):

1) Intermediate mechanics (The book by Taylor is brilliant)
2) Electricity & Magnetism (Griffiths is the way to go here, no question)
3) Special Relativity
4) General Relativity

I know you know technically need a course in E&M to understand general relativity, but a lot of Einstein's work on special relativity was motivated/inspired by ideas from E&M (and a lot of his work on general relativity was inspired by his own work on special relativity...).

Finally, on last word of warning: relativity is something you'll have to approach multiple times before you fully understand it. First, try to understand special relativity on a very simple like (Feynman has a very simple exposition on this). This doesn't take any math beyond algebra. Look at the equations for the Lorentz transformations and do some problems on time dilation and such. Next, try to understand special relativity from a more advanced point of view using Minkowski space and all the fancy linear algebra and calculus that comes with it. Then try to understand general relativity as a generalization of this, where space-time is curved by the matter in it. It's a very incremental process. If you get an undergrad degree in physics, you would probably see relativity, in some level of increasing complexity/subtlety, at least three times on your way from Newtonian mechanics to general relativity.

Though let me stress again: I think it's worth it to learn the math for the sake of the math which will free you to really focus on the physics when you go to tackle the actual ideas within. I've seen so many people get disheartened as they struggle to understand both at the same time and end up strangling themselves on the twisted mess that you get when you try to do both at once.

Libertarian nations at sea seeking to be rid of outside influence? I think we all know where this ends up. That's right: creepy little girls with glowing red eyes who are protected by walking Black & Decker tool sets gone all sorts of wrong.

If you are genuinely curious, then here is your answer, straight from the FAQ on the Seasteading Institute website: "Why not just buy an island or part of a third-world country? Our goal is to create numerous sovereign nations exploring with start-up governments, not just territory. There is no such thing as unclaimed land, so seasteading is the only option to create new societies on earth. Even if an island is unoccupied, it extends the owning country’s EEZ, including fishing and mineral rights, which are always of potential value. So even small, barren, remote rocks are claimed by existing countries and will be defended." There you have it. I'm not vouching for the content of the answer, but this is straight from the source.

The author seems to be of the opinion that cyberspace is some strange and mysterious entity that is beyond the ken of standard reasoning. From his comparisons to the I-Ching (aka Yi Jing) and Jung's synchronicity, it appears that he approaches cyberspace from an almost religious perspective (the only other alternative being that he approaches it from the perspective of bad pop science...). He even goes so far as advocating the new name of "cyberspacetime" to wrap the idea in even another layer of mystery (obfuscation?). That he buys into this strange idea is bad enough, but then he decides to criticize the DoD because they don't share this outlandish view. I'm just happy that he's not the one making national security decisions.