I just received a AR300. I’m wanting to run some simple code on the device and set up a simple TCP server. Should I use python, Node, etc?
You can use pythong. Node is too heavy for the router.
The AR300M works very well with lighttpd and php particularly if you build your own LEDE/OpenWrt 17.01.04 image. The 16 MB Nor Flash and 128MB ram is more than adequate.