Niger would get way too big...eventually. If you get it small enough you could get a few years out of it, but they do grow relatively quickly... don't count on upgrading, but if you're able or capable of doing a trade in I don't think it is necessarily a bad choice. There are many other triggers...like say a Huma Huma or picasso trigger...that grow extremely slow and could probably live out its life in a 75, however. Two maroon clowns...not unless they are a mated pair. They get fairly large as well...I would not use these. Foxface I am unsure of...size wise I think it would be ok with a picasso, but I don't know about their swim habits and such.
75 is not as big as you think, I would probably not do anymore than two of any of the fish you mentioned, as they all get fairly large. JMHO