#3: Turn on Show Recents toggle. Using this iPad dock setting, you will never get recently or most used app on iPad Home dock. Now just like Siri suggestions, On your iPad, you will see Most used and Recently closed app on dock preview.
You may try the approach outlined, which is to run defaults delete com.apple.Preview.LSSharedFileList RecentDocuments in the Terminal (manually or through your app). However I tried this and it didn't work for me (OSX 10.11), since the Preview defaults file doesn't contain this entry. You can use defaults write com.apple.Preview NSRecentDocumentsLimit 0 which will hide all recently used items, but as soon as you set that number to anything greater than 0, they will show up again. I also checked the Interface for Preview, but couldn't find anything useful.
So unfortunately it looks like this is not possible.