I have had a Niger for over five years....he only pics on crabs and snails but does not bother the other fish. Damsels are not a good idea. Besides being mean...your porc will eat them once he can fit them in his mouth.
In general, Nigers are pretty passive but they are triggers so no absolutes.
If you are going to get a large tank, you may also want to consider a crosshatch trigger. THey are expensive but a seller on ---- has listed a couple auctions in the recent past. One was for a mated pair...the other a single male. I have zero experinece with the crosshatch...not sure how well they do in the home aquarium but they are SUPPOSED to be docile....not sure you can use the word docile along with trigger in the same sentence