You can download the manual for the mps sensor
here. It should answer most of your questions.
The tubemeter is not necessary when you use the mps pressure to get the value.
You will need 4-pin aquabus cables and a y-adapter to connect everything to the aquaero 5.
You should not place the flow sensor directly behind the pump since the turbulences in the water might distort the measurement. You can place it anywhere else. The flow rate is always the same at any spot.