SC2Mapster

Using that field affects how high it sees. You will find that altering this field allows units to see over los blockers of a lower height. It also affects the height missiles start from.

I find it best to start from scratch and not modify existing maps. Still I can take you through the creation process. For a start read some of the tutorials on attachments by ProzaicMuse.

The los blocking is part of the footprint. Just have the missile impact use a Create Persistent to spawn los blocking units with a timed life that are unselectable and have a height of 4 else air units can look over it.

Getting the cursor to show properly will require a Model actor that has the basic scope follow SOp created on the ability cursor and destroyed on cancel. You then need to give it a SOp forward vector to get it to face the caster and then attach your other visual models at an offset to it.