I had a go at this too, although there were a few aspects of the rules I wasn't sure about. I was killing all Elites, but maybe we were allowed to bypass them if desired? In places, bypassing would've been easier (though boring). That's how I came unstuck actually. On my ascent in the main facility, I'd got back to the Hunter chamber and I was in good shape so I went gung-ho into the short passage containing an Elite with Grunts, and just before I could manage to finish off the Elite (a red), I got killed.

But that brings me to another rule aspect I wasn't sure about. What if I tag or needle an Elite, and the bang happens to kill non-Elites too? I was assuming that was forbidden, because I'd be responsible for their deaths even though I didn't target them directly. So instead, Elites had to sometimes be carefully picked out using non-explosive weaponry. That's what I was trying to do when I got killed. It was troublesome with that Elite because he had a mob of Grunts around him.

: I had to cut my session after a lucky/unlucky checkpoint on the upper tier
: where the gold elite is. Lucky that i pulled the checkpoint in the room
: with grunts and the 2 elites nearby, but unlucky that i only have a single
: health bar remaining.

Used up both the medkits below?

: I also learned just how much i crave killing covies, it is so
: hard to stare them down and let them live on.

Yeah, had to keep reminding myself not to shoot the minors. Certainly goes against instinct.

: Bonus note, after getting the hog at the crashed pelican site and driving
: past the beach, i was suprised to see the storm the beach battle was still
: raging on - cool stuff!

Yeah, it freezes when you get far enough away. You can potentially return with a rocket launcher, to rejoin the attack and finish it off in novel style.