Endermen always vibrate when they're angry
I don't really know what you're tryna point out here, but items despawn after 5 minutes (when the chunck is loaded where the items are in) of them laying on the ground. When you die, all your items are dropped so they then the despawn timer of 5 minutes
Could it be that the skin you're trying to import is either corrupted or in an incompatible format (skins need to be .png files and need to be a size of 64x64)
You can try my attachment here, if it still doesn't work then i dont know what is causing it:
[media]
This is intentional. Particle effects are intentionally turned off for Bad Omen (it whould be silly if it wasn't imo), and the icon is there to let you know you have bad omen.