I've been running a bunch of Pi's for years now, and the biggest problem I've had is the Pi itself dying: 24/7 usage is hard on a small device. I've also found that stable power is essential, and to that end I've always used 5v 3a branded power cubes, plugged into a pure sine wave UPS. Choice of micro-SDHC cards is important and I ended up getting ATP industrial cards (https://www.atpinc.com/products/industrial-sd-cards) - expensive but really long-lived. Finally, using RPi-clone (https://github.com/billw2/rpi-clone) on a regular basis has been a life-saver. I clone to Sandisk Extreme micro-SDHCs and can recover from an outage in minutes.