Hi there. There are a few options for you regarding your list. This is from personal experience and not just "text book" theory. Everyone will have their own experiences and advice.
If you're set on a Harlequin Tusk; you can try looking for a juvenile or smaller one. The smallest I've seen are approx. 2" in length. Watching it grow and morph in colour over time is very cool.
As for triggers; most of the genus: Xanthichthys are considered to be a little more docile and "Reef Safe" with caution. These include - Blue Throat and Sargassum (both of which I have); Crosshatch, Kiri Tirgger (now known as Xanthichthys greenei. At the end of the day...they still are trigger fish....with teeth. Mine have never looked at any corals or even the smallest of shrimp (ie. harlequin). However; I do make it a point to keep them well fed. I've extended the periods of time and frequency of feedings to acclimate them to longer periods without food....no missing inhabitants so far. Except the odd snail. It's an innate response for them to grab and chip away at the odd snail. Tehy will want to grind their teeth on something hard (like a beaver). In keeping these fish; I'm more than willing to sacrifice a few snails.
I'm also keeping in my display (120 Gallons) a Purple Tang, and Red Lined wrasse. All inhabitants seem to get along well and have been for an extended period of time now. It is possible.
Good luck.
I can share some pictures of my collection if you wish. Let me know if you want them posted on your thread or sent to you privately. Cheers.