Import/Material Setup

Import the vanilla item of choice into Blender. I’m using the Ravel Keeper’s Chestpiece of Casting for an example here - because this skirt has MANY parts and is very intricate. You may see that your textures immediately look weird. That’s normal for vanilla. I don’t really understand why SE sets up their items the way they do, but they do. We’ll fix it! 
 
 
 
 Go do your Properties column or tab - this is the tab that contains all of your vertex groups, materials, armature etc. You want to click on the button that looks like a circle with two black and two white parts in it . (marked on picture as 1) 
 
 My new blender layout is aggressively pink, so it may be hard to see, but here it is on mine, at the bottom. 
   
 From there: go to Settings and Viewport Display , and change Alpha Blend to Alpha Hashed . This will fix the strange shapes and backface collision issues that you have on the original. (marked on picture as 2) 
   
 Some people click “Backface Culling” in settings but I personally don’t . I like to see where the backfaces are on my outfit, so I can figure out if I need to remove them or leave them alone. That is a personal preference, and one I urge you to play with. 
 
 At this point I import a second copy of the vanilla item I’m working on and keep it in a collection labeled “backup.” This is important because sometimes I mess up. Additionally, this can be useful if you ever have a problem with the model’s normals, as you can copy data from the backup.