3-pin pump connector and 4-pin fan header is NOT a problem here. But Do change so that the PUMP is in the CPU_FAN header, and the rad fans are on the CPU_OPT header. Then ensure the CPU_FAN header is set to PWM Mode. Its Fan Speed Control should be set to Normal.
To help you understand why, some details. First, because of the design differences between an older 3-pin fan and the newer 4-pin type, when you plug an older 3-pin fan into a header using the new 4-pin PWM Mode of control signals, that older fan cannot have its speed controlled. Instead it always runs full speed. And it happens that is exactly what you WANT to happen with this AIO system. Its pump is wired just like an older 3-pin fan, so it runs full speed when done this way. Second, the CPU_OPT header really is just a mirror of the CPU_FAN header and does exactly the same thing. So when the rad fans are connected there, they ARE fed the correct speed control signals and CAN be controlled because they are the newer 4-pin design.
Lastly, the CPU_FAN header has an important second function. Although it does not use the speed of its "fan" (in your case, the pump) to control that speed, it DOES monitor that signal for NO signal, which would indicate failure. If that happens, it pops up a prominent warning on your screen so you know you need to fix that. But MOST mobos do much more with the CPU_FAN monitoring process. Within a short time of detecting failure there, they will shut down your system entirely without even waiting for the temperature sensor inside the CPU chip to show high temps. This is to protect the expensive CPU chip from permanent damage due to rapid overheating, which is exactly what happens when the CPU gets NO cooling. Further, it may refuse to let you start up if it gets no speed signal from its "fan" at any power-on. Now, with an AIO system, the most critical component is the PUMP. If it fails there is NO movement of heat from CPU chip to rad and NO cooling of the CPU. But if the pump is running and one or both rad fans fail the cooling is poor and the CPU may overheat slowly. This would be detected by another safety system and cause slow-down or shut down later, but no CPU damage. So the PUMP should be the item connected to CPU_FAN so that protection system can do its job.