We don't but neither do universal simulations. Maybe I should have said finite-state turing machines. With a vast enough universe, the finite # of states won't matter much when it comes to producing life. What fraction of the information in the universe are our bodies, or if you go down further to simpler smaller species, the fraction gets smaller. It's tiny.

2) Yes, basically a flat torus. Not the most beautiful topology.

3) Yes, I think locality is the right approach at least for starting out. This project is iterative so nothing is set in stone.

Thank you for the questions and comments. I guess I left quite a bit out. And right now, I'm in the middle of a lot of design decisions regarding fusion and decay. It's not easy to build a universe, even a simple one.