did the predator kill jim hopper and all of his men? was the man executed just prior to the attack on the camp one of hopper's men? if not who was he?
Yes, the Predator killed Hopper's men, that's why half of them had been skinned while the other half simply vanished without trace.
As for the guy executed at the camp, that leads into question #2...
what was it that the CIA was after? was the russians about to capture a predator? someone said something about "something big was about to go down here". was that the big thing?
The rebels in the film were gearing up to invade a neighbouring country, one presumably friendly to the United States. The Russians were there to equip and train the guerrillas. The CIA's mission was to stop this invasion from happening. The hostages Dutch is hired to rescue were not cabinet ministers, as he was told, but CIA agents working for Dillon, who were presumably scouting out rebel locations as part of their mission when they got shot down. It's one of these agents that we see get executed immediately before the assault.
The "something big about to go down" was the rebel incursion over the border. The US and Russia were all over South America in the 1980s, discretely (or even not-so-discretely) backing various regimes friendly to their political ideals, and its this situation the film is tapping into.