The fact is, everything you have described so far points away from using a microcontroller.
There are some functions for which a microcontroller is the perfect solution. This simply is not one of them.
You want a prompt response to simple input variables. The major two parts of your task are design the circuits to measure certain parameters and to execute certain control functions. You simply connect the first part to the second part - you have not described any reason to introduce a microcontroller between, except to unnecessarily increase the complexity.
Further than that, if you introduce a microcontroller, you are then responsible for making it "fail-safe", lest it suffer a program "crash" and baulk in such a state that your system "runs wild" to its maximum output with no limit.