I would start off running the onboard diagnostics to see if an error pops. Restart your system and press the ***D*** key.
Reference: [https://support.apple.com/en-us/102603|Mac startup key combinations]
It does sound like your system had a liquid spill given the symptoms. You likely will need to open the system to inspect things.
As far as the kernel_task this is effect of SMC trying to protect your system by reducing the CPUs clocking, which you’ve noted causes the system to run slow down. The fact your keyboard and trackpad are not working is were you need to focus in on the logic board keyboard & trackpad connections.