A couple things;
Is a "cup 'o sand" really a valid long term solution for a fish requiring substrate? I've observed behavior of burying wrasse in QT with the pyrex bowl of sand, and while they find it quickly most nights, there are some that I have spent an hour plus watching the fish desperately race around against the bottom glass trying to find the sand to dive into, for whatever reason they couldn't locate, and they don't look very calm while attempting to do so either.
You can avoid every major pest a SPS person will run into with care and attention to your new additions, unless the wild west is being thrown in there (mariculated / wild collected colonies). The 170 is essentially a nano tank, shoe-horning fish that don't belong in it doesn't seem like a great long term plan for success. Hobby is full of trade-offs, going smaller is much harder than larger in regards to "workhorse" livestock. You've had all the best solutions proposed already, and it's basically one at this point - pinkstreaked p. ataenia.