Both Flow Simulation and Structural stress analysis will attempt to create a mesh to formulate a means of solving equations. The level of detail of your assembly (especially the tyres) will mean the analysis will be very slow, if it can run at all. You really need to do a lot of simplifying before you can get anything meaningful out of the software. You should set goals/objectives for the analysis and this should allow you to think what you can simplify without compromising the results too much (i.e. if the tyres are not a concern, then just have them modelled as cylinders with no surface textures). You are also correct about flow simulation, you need all the items as solids as Flow Simulation attempts to find the boundary between the solid and where the surrounding fluid/air will be. A surface body may have a tiny gap, which Flow would interpret as a means for the fluid to enter. All models should be watertight with no overlaps/interference. Again flow will need to create a mesh in all areas- solid and fluid so the more tiny details, the more demanding it will be for the PC and getting any sort of result could take days. As for help for this, have you tried MySolidWorks. On here there are likely some introductory videos to the subject. One of the key skills in analysis is creating yourself a model which will give efficient results. Having the base model as a non native SolidWorks file (i.e. a parasolid) will make this harder as you cannot just turn features on or off, but it won't be impossible.
There will be no quick answer I'm afraid on this but hopefully some points to consider.