If you want a truly comprehensive experience, then watch every episode.
Agreed. To get the full experience watch every episode of every variation of Trek. That's the only way you are going to determine what is 'essential' to you.
But if it isn't feasible to watch every episode, then what I would recommend is picking up the Star trek Fan Collectives
and the Jean-Luc Picard Collection
, along with the Star Trek movies. You get a pretty good cross section of some of the best episodes from the various series in the Collectives, except maybe for DS9. DS9 is so serialized (much more than any of the other Trek series), that it is impossible to get a good sense of the show in just a handful of episodes, and the DS9 mirror universe episodes are actually some of the worst DS9 episodes, in an otherwise great series. In fact, Eater, many of the episodes you have listed, are in those fan collectives.
But if you can't do all the Collectives, the "must see collections" IMHO are The Borg, Klingon, Q, Time Travel Fan Collectives, and the Jean-Luc Picard Collection. You can find many of those collections used in a second hand store, or online pretty cheap, now, as long as you don't care its not blu ray.