Meta keywords serves no value as per Google, but other search engines still using it. So if you're targeted other search engines then you should use it.

Having a meta keyword tag (even if ignored by major search engines ) is better than not having it. Also do not put much effort optimizing it due to its low consideration.

Nope, it used to add value, but not anymore.

Those days (waayyy back) sure is useful..But now I agree this four up here. You need to be more vigilant ;D.

Generally no, but be sure to write a compelling meta description in order to tell users more specifically what your page is about and to increase CTR.