Almost all of those fears you enumerate are unfounded. You won't kill a processor through overheating if you forget to plug in a fan. Not properly securing your CPU heatsink only really poses a risk to the GPU that it could fall onto. Likewise for your concerns about the SSD's temperature: it'll throttle itself and shutdown if necessary, but the latter won't happen even if you're blowing 85°C air from a GPU directly onto the SSD—I've tested that with most of the M.2 NVMe SSDs on the market. There are essentially zero connectors inside the PC that allow for the mechanical possibility of connecting dangerous voltages to the expensive components.