When you export, select only the tank objects and then choose Only Selected in the export options. That’ll stop any hidden objects, cameras, or whatever from also being added to the file.
As for textures, you can hit the Edit 3D Settings button on Sketchfab, head to the materials tab (the icon looks like an image) and upload your texture as the base color. Click on the different parts to switch which object is selected if you have multiple.
That model is looking good!
