To make the explosion you don't even need to make a unit. Just do Create Model At Point and pick whichever effect you want (some explosion effects need to be Killed right after they're created).
To look for a decent explosion effect what I usually do is search through the models in the data editor, searching for "impact" and right click on them and say "preview model".
To kill the units near the explosion, just say:
Pick Each Unit In Region Matching Condition
For the region, use your region: 1[I]
Then, inside the block say Kill Picked Unit.