threejs-loaders

Use GLTFLoader from three/addons/loaders/GLTFLoader.js and call loader.load with the model URL and a callback. The callback receives a gltf object whose scene property you add to your scene, and whose animations array can be played with AnimationMixer.

Create a THREE.LoadingManager and pass it to each loader's constructor. Set manager.onProgress to receive loaded and total counts for a progress bar, and manager.onLoad to detect when all assets finish.

Yes, GLTFLoader supports Draco compression through DRACOLoader. Create a DRACOLoader, set the decoder path to the Draco decoder files, call preload, then pass it to gltfLoader.setDRACOLoader before loading.

Use RGBELoader to load the .hdr file, set texture.mapping to THREE.EquirectangularReflectionMapping, and assign it to scene.environment. For PBR quality, prefilter it with PMREMGenerator's fromEquirectangular method.

The texture likely has the wrong color space. Set texture.colorSpace to THREE.SRGBColorSpace for color and albedo maps, and use linear color space for data maps like normal or roughness textures, then set needsUpdate to true.

Yes, wrap loader.load in a Promise that resolves in the onLoad callback and rejects in onError. You can then use async/await and Promise.all to load multiple models and textures concurrently.