This task ahead of you is difficult, you were not given a "watertight" model to do a flow simulation. Watertight models are required for flow simulation.
You will have to fill all the gaps with small surfaces, and then knit those to join. Fill Surface is good for doing this to fill in any size hole.
I suggest changing the way your model displays, and turning on show edges. Also, under Tools>Options>System Options>Display/Selection>Show open edges of surfaces in different color. That will make it more clear what is going on, and where all the open edges are. If you do, take another screen shot and post that.
Dave, before you can do anything with your surface model, you'll need to address those surface gaps and imperfections.
Given how many patches the model has, I don't envy you that task.
Final note. If your step file was created with a specific unit, SolidWorks applies that unit whe constructing the model, so you shouldn't have to scale it. If your step file was created without units, then you can tell SolidWorks to assume the units of the step file are the same as your document template so that you don't have to add the scale feature.
To access thsi dialog, click the "Options" buttun in the Open dialog box after you've selected your step file.