1. I just tested seeing items like bamboo salvaged shelf skin and iced ak skin - i own both of these, but once i turn the config option "Allow Owned Skins" to false I dont see them any more.
2. You may have to delete the PlayerUsageData.json in data/skinner, this file can't be filtered easy as we can't get data for offline players.
3. If you backed them up you can move them to the data file. The next update will move them automatically.
4. Set "Allow Skin sharing for teams" to false