Don’t add them to IgnorePkg in /etc/pacman.conf, just don’t panic over warnings.
No, see above for the way to do that.
You won’t. That is why you shouldn’t.
You should want to know that those packages have problems that need addressing. Putting it in IgnorePkg so you forget about it doesn’t seem like a solution.
Also, it will only work with certain helpers. Some helpers don’t honor IgnorePkg for AUR packages.