Your model is in the correct format, but the faces are way too much as you can see below. This would be find but with any mistakes or minor issues with the CAD, the mesher will freak out and give errors as you have encountered. Fixing it is also near impossible in this current format as you will not be able to tell where the issues are.
The mesher (snappyhexmesh) requires a very well defined geometry in order to produce a mesh that is of good quality. This is the first criteria that must be fulfilled.
My recommendation would be to combine the surfaces and re-upload a watertight (no holes, no outcropping and generally good CAD practice throughout) geometry. For example your back area should be a single smooth surface rather than what it is now, just a bunch of surfaces together. This is not good CAD practice as mentioned and is completely unsuitable for CFD use let alone meshing. You can also try the STL format once the CAD issues are fixed.
You will also need to simplify your geometry significantly. All these excess details not only make it very difficult to ensure your mesh will be of sufficient quality for simulation, but for the added difficulty and work needed to get them to mesh well, your results will also not differ significantly enough. So remove as many sharp edges and keep your detail to a minimum.
After these fixes, we can look into meshing again.