A little bit of help for your first question, with this answer targeting the loading of GLTF format.
Maybe try my GLTF WebGPU Viewer with the StainedGlassLamp KTX2 example from KhronosGroup. The easiest way to do the test is to actually copy / paste the following link into the URL option of the viewer:
https://github.com/KhronosGroup/glTF-Sample-Assets/blob/52c9f0e473a523057135281b19d12b768e2f7eb7/Models/StainedGlassLamp/glTF-KTX-BasisU/StainedGlassLamp.gltf
Also, check this topic for some additional info on the viewer itself and its picture indicating whether WebGL2 or WebGPU is being used.
You can check the viewer’s code, which is pretty much the same code I used for WebGL2 renderer.