To your other point, yes it is definitely possible to create your own AR launcher. There is a thread about that here Custom launch AR button
I’m realizing now that topic is a bit dated, however the information from Google and Apple references in there can still be helpful. The newer and more efficient approach would be to pre-export the AR files and use our layers API to pass the configuration to the API. The format parameter would be ‘usdz’ or ‘glb’ depending on the device being used. The contingency is that the items must be pre-exported and exist in Threekit to be available in the layer service.
https://{env}.threekit.com/api/layers/layer?format=${format}&bearer_token=${token}?assetId=${assetId}&assetLayerConfiguration=${encodeURIComponent(JSON.stringify(configBody))}
This API call should return a fileId you can use to get the file directly from Threekit https://preview.threekit.com/api/files/${fileId}/content
I have created several myself so if you need any guidance I am happy to help.