Lua is cute as a lightweight extension language that (with LuaJIT) can compile to very fast code. But the language is rather stripped down in order to keep the memory footprint small and the interpreter embeddable. It also has too many automatic conversions in my opinion (trading reliability for convenience), though that's a subjective matter.
Lua is mostly used as an extension language in C and C++ programs, possibly running in quite small systems (meaning like 1 meg). If you've got a big machine (32MB counts as big in the embedded world) you are probably better off with a language with more creature comforts. PHP has a lot of built-in libraries including database connectivity. I hate the language but I have to concede that it's very easy to get started with.
Next up would be something like Django/Python, or Ruby on Rails. Node.js was trendy for a while but I'd suggest staying away from it as it will rot your mind. Go (golang.org), now trending up, is much saner and should give performance at least as good. I'd consider it a bit more "advanced" than something like Ruby though. I don't think you really have to worry about performance for an app like this, due to its expected relatively light workload. A simple Python or Ruby CGI might be the lowest fuss implementation technique.