1. Do you know what the name of the task manager is that is installed? Maybe you could use an app like sktools or another uninstaller app that would allow you to uninstall that task manager. I know the one you are looking for in the upper right is the htc task manager. You could probably do a search of the registry using a reg editor like PHM that has a search/find function that you can search for the name of the task manager and then disable it there and then remove the files using file explorer or total commander.
2. Do you know if it only makes that sound when you press the end key or does it play the same sound when you push the buttons on the d-pad or camera? I know that on the stock rom all of those buttons play the same sound. I'm sure you could find those sounds in the registry and change or disable them. Probably the easiest way to disable all key sounds is to go to sounds and notifications and uncheck key sounds/taps or whatever it is called. The default sound on the stock rom I believe is called "type."
3. Not sure on this one.
I am curious so I am gonna try to find out.