Hi there, I'm the author (of the blog post, not of the achievement itself)! So glad this is spreading. Feel free to ask here or on the post for more clarification if stuff is too unclear
My hope is that by reading only the amount of background on the blog already in the Waterbear post (referenced immediately in the introduction), you have all you need to grok the post. But that's certainly an optimistic hope, and maybe unfounded.
I have read quite a bit about GoL before over the years, programmed and experimented with it and many variants etc But never tried to build a.. well, it's high level programming in GoL isn't it, or like building UNIX tools in GoL and doing cool things with complex combinations of them. I had my mouth open in amazement reading it. Bunch of maniacs. This is an extreme sport. Thank you!
Advanced gol is just getting past that first hurdle of understanding the densely compressed info behind the jargon. And it doesn't ever need to be done for all of the concepts. You can be versed in just one. I started out in a super specialized corner in self constructing spaceships. That said I'm a bit of a whiz in other areas so I can't be used as evidence that it works for everyone..
Probably I'm a good case in point. I'm definitely not a particularly clever mathematician, but it seems like it's possible to understand any new Life technology just by tinkering with the pieces for long enough.
If anyone wants to follow along with that kind of learning process, just start working through the Life textbook that kryptiskt mentioned. (Full disclosure, I'm one of the authors.)
Even though in my life, I can't make the time for doing something on the grandiose scale required, I can live vicariously through reading about your sheer dedication and intellectual effort expended.
RCT is basically one very unreasonable end of a wide spectrum: you can use a very small number of gliders to build something, as long as you're content to have the construction take a ridiculously long time. Conversely, you can build that same thing in a lot less time, but it will take a lot more gliders.
The glider positions might very well require more storage than the desired pattern itself.
But the number that says how far apart those corners are from each other has very roughly half a million digits. The exact number depends on exactly what pattern is being encoded by the RCT pattern -- I think the example construction of Alan Hensel's decimal counter pattern needs somewhere around a 450,000-digit number.
There are some optimizations underway to decrease that number by a few percentage points, but it's always going to be a very big number!