I have done Challenges 1,3 & 4. I have no idea how to set the air unit to prioritize units that can attack ground for Challenge 2. And 5 is just a scourge.
Continuing the Sentry/Carrier saga
Deals 30 damage in explosions. Any ground units in the target area or enter within 6 secs will be burnt to death and run away from the centre. Notice that the explosion damage and the burning area spans across cliffs. Also notice that large units like Thor, Ultra and Colosus uses a larger fire model. (Those are the largest ground units I think)
Target a point, then a carrier warps in above the sentry, lands, loads in all the player's ground units within 3 range of the sentry. However, units moving into 3 range after the carrier landed will not be loaded. Once all units are loaded, the carrier rise up and unload cargo at the target point.
Simply summon a carrier which fly to the target point and create 8 paratroopers (Zealots). Not paratroopers actually as they uses kind of jet pack rather than a chute. Notice that the Zealots can't move, attack and are considered air units before they land.