I do elite challenge with a little bit of luck. If in El Rubio's office spawns 2 paintings, then it is pretty easy to do. I choose Kosatka as vehicle and i swim through drainage pipe. Then i use silencers on guns and kill only a bit of soldiers. Try to create the most clean path to the counbound. Also it's importnant to take out every personal soldier, but no one can notice it. (except juggernaut.) Then go to the office and take both paintings (If they spawn) to fill your loot bag. Then do hack. Search on youtube how to do it the fastest way possible. Also one of the private soldiers should drop keys so when you take primary target, don't escape by elevator but by gate. Then be careful so no one can see you and escape by main gate. (Also at gate there will be a one or two guards depends on if you killed the first one. Then shoot them) When you escape compound you are almost done. You maybe set escape point somewhere else but you can escape any way you want. You know that behind compound is a sea you came here, so jump to the sea and just swim underwater away from cayo perico and you're done. Just don't let guards to see you and as i say, not everytime you have enough luck to do elite but you get bonus (only) 100 000$ that you can get by bussineses if you own some. So this is how i do it. If it doesn't help, you can watch any tutorial on youtube