The Pressure Sensor MPS CAN be configured to read the loop water pressure, OR to read the reservoir water level, but will NOT give a water flow reading.

The Flow Sensor MPS CAN be used to measure water flow in the loop, but NOT the reservoir water level.

If you bought one item from each list linked above, you should be good to measure reservoir level and the water flow.

Yes indeed, you are good to go.

For completeness the functional parts are the same by both.
A metalmembrane that separate two chambers and a electronic that measure the deformation of it.

To be really accurate the pressure sensors can be used as a flow sensor because the essential parts are the same.

You can actually create the only zero resistance flow meter by using an existing restriction like say the CPU block and connecting the pressure sensor lines to either side of it. You then need to create a fully custom calibration for your flow sensor as it naturally will be nothing like the stock flow meter configs.
The trick is matching the restriction you use to the right sensor. It is certainly not for beginners though like the actual flow sensors can be.