The "normal" way that the CPU cooling system on a mobo operates, when used with a liquid cooling system, is this. The PUMP unit operates constantly at full speed to move the liquid around the loop. The FANS on the radiator (where heat removal actually happens) have their speeds controlled automatically by the mobo CPU_FAN header according to the actual TEMPERATURE measured by a sensor built into the CPU chip itself and fed out on one pin. The automatic control system on the CPU_FAN header has a pre-set temperature target and some loop tuning parameters for this operation. MOST mobos also allow you to opt instead to use your own custom fan "curve" (graph of fan speed vs. measured temperature) for rad fan speed control. Within that you can set a minimum speed (they usually prevent you from setting it so low that the fan can stall) at your lowest temperatures, and higher speed for higher temps.
IF one were to create a cooling control loop for such a system that changes BOTH the pump speed (controls how rapidly heat is moved from CPU to rad) AND rad fan speed (controls how rapidly heat is removed from the liquid), the two heat removal components with different response times are VERY likely to "fight" each other with actions to counteract each other. So the normal system keeps ONE of these unchanged - the pump speed - and manipulates only the FAN speeds. A few such systems allow minimal pump speed changes according to temp ranges, and with very slow response characteristics so the fan speed system can adjust smoothly, but not many do that.
So, the system present already in almost all mobos DOES control heat removal, but uses a temperature sensor in the CPU chip, not one in the fluid loop. That is a more accurate guide to the CPU's cooling needs, and it has the advantage of very quick response to rapid heat load changes. It DOES offer you the option of customization of the "fan curve". And it DOES operate at the mobo hardware level, irrespective of OS. Some (but not all) AIO systems combine these elements with their own software utilities that communicate with the mobo and take over the control system, and that does depends on the OS. But not all do that. Clue: if the connections for a commercial AIO system tell you to connect the RAD FANS to the CPU_FAN header, and do not instruct you to download and run their proprietary software, then control is being done solely by the MOBO's automatic system as I describe above. But I realize that probably you do NOT plan to buy a commercial AIO system, and are doing your own cooling loop system.
So, much of what I believe you are trying to achieve can be done using what your mobo already has. Perhaps I'm missing something here. But consider the option of NOT dong the work to create your own.