thanks for the answer... I don't have energy costs because I have a solar system... the firmware was like security more... for example if a fan fails the firmware has settings that no longer turn on or restart and notify by telegram or email once that s9j will be in my warehouse and not in my house... that is, I have more security settings and others than antminer's firware.
The stock firmware will NOT mine without two fans running, there is really no added "security" using custom firmware, in fact, all decent firmware will stop mining when the miner's temp gets too hot "including the stock firmware", you can control the fan speed on all firmware versions, for your case, I don't see any benefit from using custom firmware, you will just have to pay fees probably for nothing.
What you need is monitoring software, which isn't something you flash on your miner, it's something you install on a PC that is located in the same LAN as the miner, you configure the software to send you an email/telegram when something happens, the stock firmware is compatible with all these software, I recommend AwesomeMiner, there is also
Mineitor which I have not tried but seems like a robust software.