I don't think the trigger will mess with the corals....but will go after any mobile inverts like snails, crabs, and shrimp.
If you are look to put a lot of fish in 75g tank, get a refugium. I have 75g tank with a 30 gal refugium.
Personally, think the Heniocus will get too big for the 75g and become aggressive. I know of a person that had a Majestic Angle killed by her Heniocus when it got to a bigger size. Both fish were same size. I would worry about the trigger becoming too big for the tank. Bluejaws/Blue Throat triggers are usually peaceful to other fish, but one can never tell what will happen when the environment becomes too small for comfort.
I do not like tangs of any kind in tanks under 100g (not counting sump.fug size). Some have had success, but tangs seem more terroritorial in smaller tanks.
Personally, I have a pair of Bartletts Anthias in my 75g and have no problem with them. They have been there for over a year. Dispar Anthias is another one you can try, but be warn, they are jumpers and may jump out of the tank in the middle of the night.
There are a lot of fish you can put into your 75g reef tank.
Here is a list of fish I have in there now:
A pair of Bartletts Anthias.
A pair of Yellow Claown Gonies.
A pair of Carribean Neon Gobies.
Coral Beauty.
Foxface. (Eventually will be the biggest fish in the tank).
Black Sailfin Blenny.
Pink Spotted Watcjman Goby.
Randalli Goby.
All do well together and are peaceful. I do not plan to add any more fish to my tank. From this point on, I will be removing most of my soft corals and switch mainly to SPS, LPS, and a select few soft corals like zoanthids and mushrooms.