Thanks so much Scott for your comment and ongoing support! Also, I really appreciate the donations! I'm glad to hear that. I really enjoy making things like this, probably almost as much as I do playing with them. It's nice to see that others are having fun with them too.
I love Lua too, and good news, that's what I'm using. For everything before this project I was using Love2d, which is a framework for making 2d games with lua. For simple things I would recommend it. The wiki is really simple and there is a big enough community that you can find your questions already answered somewhere 9 times out of 10. I definitely tested its limits at times. I don't know much about Codea though.
Lua is actually plenty fast because of luajit. For Evolpedal 3D I needed some real 3d physics to make it work, so I went looking around for other open source engines. I found some good ones but ultimately settled with Urho3D because it also has lua bindings. It's incredibly snappy and intuitive. I'm likely going to stick with it even if I do more 2D games. Leadwerks also uses lua but it was pretty buggy and slow. There aren't a ton of options for 3d game engines with lua bindings. I could always get better at Python or C++, but this is just a hobby so I'm focusing more on what's fun for me.
Just looked into Codea a bit. It looks like you should be able to make similar simulations with it. The thing to keep in mind is that if it does have a bottleneck somewhere it may hinder your progress. Some of my other ones, like Polysporia, can easily get laggy with lots of lifeforms. That may also be the case with Codea, or it may be worse. If you know it pretty well already I would push it to the limit and then only then think about switching.