Any brush that is not otherwise an entity, is "worldspawn"...regardless of whether it's detail or structural. Most of your map is worldspawn. A brush being detail or structural has nothing to do with it being part of the worldspawn entity.

It is true that the "hull" of your map, any brushes that are exposed to the void, must be structural.

Entities are always detail anyway, except func_group I assume, those should be more or less ignored by the compiler in that sence. You don't need to mess with them.

Curves are also always details, and needn't/can't be altered.

ANY shader can have structural specified in the script. That means certian textures will always be structural. The entire brush must be textured with textures having matching parametes for it to work properly.

Hint brushes are structural (it's in the shader). So is caulk and a few other "tools" shaders.

When you first add a brush to the editor, it is set as structural. So you should generally only have to change it to detail if at all. If your unsure what should be detail and what should be structural, see my post in the sticky thread about r_speeds and r_tris (quite a few pages into it).