Simple Enough: Keyboard and Mouse without Cables
It's not difficult to set up wireless I/O, so long as you avoid devices with infrared transmitters. My preference is combined mouse/keyboard adapters, which only monopolize one USB port for both peripherals. Some of those adapters are even Bluetooth-compatible, facilitating communication with other hardware, too.
Home Network and Internet
Again, this is pretty standard gear. I did run into signal strength issues with the locomotive down on the floor though, requiring me to replace my first Wi-Fi adapter with a high-power model that gave me flawless reception in the 5 GHz band (802.11a).
A moving locomotive deserves its own video camera! For simplicity's sake, I'm using a normal webcam, though it'd be easy to use a more discreet camera mounted inside the chassis.
A Skype session between my desktop and the locomotive demonstrates flawless 720p video. Really, this is just a fun little demo.
We need to get rid of the audio and video cables so the train can move freely, though. Moving on.