It is not necessary to use mass flow inlets in incompressible flows because when density is constant, velocity inlet boundary conditions will fix the mass flow. 

Outflow boundary condition used to model flow exits where the details of the flow velocity and pressure are not known prior to solution of the flow problem. They are appropriate where the exit flow is close to a fully developed condition, as the outflow boundary condition assumes a zero streamwise gradient for all flow variables except pressure.

For the calculation of pressure, try to apply bernoulli between two points. But I suggest try using velocity inlet and outflow boundary condition at exit.