Glenn, you don't say what version of ANSYS you are using. I opened your file with 2019 R2.
I am also learning Fluent, so I am willing to be corrected by the experts. I believe the correct selection is the Pressure-based solver, not the Density-based solver which is better for air flows that have extreme pressure gradients that cause the density of air to change, such as supersonic flow.
A Steady State solution is always a good place to start a study.
CFD needs good quality elements. Skewness is an important quality metric. You have 10 Pyr5 elements that have a skewness of 0.991 and that value can ruin the whole simulation result.
You ideally want elements with skewness < 0.75 so slice and simplify the geometry until you get there.
It can happen that during the iterations to a converged solution, some cells on the pressure outlet might have reversed flow, but as the solution improves and the residual errors are driven down, the reversed flow will probably resolve itself.
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