Custom Minimap:
- Create a 32 bit Targa image (*.tga) using following resolutions: 128x128 or 256x256.
- Run World Editor and then open Import Manager.
- Click "Import file" button.
- Point to your TGA minimap.
- When image appeared on the list, double-click it.
- Click "Custom path" checkbox.
- Remove path string and type "war3mapPreview.tga".
For Loading screen search tutorial.
If you want more info, search it in (4)Monolith.w3x in "Warcraft III\Maps\FrozenThrone\Scenario\" directory.