How to fix WoW models in photon workshop
I believe you've identified the primary problem with this model. The single surface features are going to interfere with printing this object.

The image above is the result of loading the model into Autodesk Netfabb. The red segments are reversed normals, but also single surface components. There are others, visible when rotating the model.
One portion is uncertain, above the flap on the back. It could be a component of the flap or a reversed normal of the body's back.
To resolve this problem, it would be necessary to add thickness to those features.
I loaded the model into Meshmixer and identified one feature, the rear flap. It's loaded with reversed normals when viewed from the &quot;outside&quot; or rear of the model.
Using the select tool, it was easy enough to highlight those triangles and proceed to Edit, flip normals. That was followed by Edit, Extrude, to a thickness of -0.02 mm which presented this result:

There are a few &quot;floating&quot; features in the model. One which pops out is over the protective garb over the shoulder. Those would have to be anchored by adding features or moving that specific feature to properly intersect the body.
There are a few others, zero thickness portions that resemble solar panels. I suspect they are artifacts rather than intentional model features. Those can be removed in Meshmixer using a similar method, Select, Edit, Delete
The hanging hook is a collection of intersecting faces and present a challenge. It's not my model, but I'd be inclined to completely remove that feature, or remove most of it and add a simple cylinder to attach it to the model.
There are programs other than Meshmixer which will allow one to perform such manual repairs/modifications, but my skill set does not include presenting the answer for those packages.