You don't really need an RTOS to do something like this safely, but agree you need more firmware knowledge than "tinkers with Arduinos" to stay clear of possibl

You don't really need an RTOS to do something like this safely, but agree you need more firmware knowledge than "tinkers with Arduinos" to stay clear of possible unfortunate failure modes. You definitely need to build in some interlocks and/or other sanity checking. Similar with the PCB's, many of the better dev boards are pretty decent, the problem comes with poor connections designed for easy access, etc. This can be resolved without spinning a new board though, or perhaps designing a simple extender.