Definitely lots of room. However I'm sure you've seen some of the recent threads about Nigers getting aggressive after a while as well as their max size? (I only mention this because of how you were put off my the Koran).
There are two real concerns about deciding if there's "room" in a fish tank. Most importantly IMO, is load ability. Can your set up handling the load? Once you go over about 90gals, it starts to be become more about the bio-load then say, space. What sized skimmer, refugium size, water changes, etc. The other thing is 'usable size.' You can have a huge 400gal tank, but if you have 2 Queen angels that occupy both ends of the tank and don't let the other fish do squat, your available size is very limited.
None of the fish listed:
snowflake eel
lemonpeel angelfish
niger trigger
checkerboard wrasse
set up and maintain a territory. So if you have a decent skimmer and good water change schedule, you should be good to go for more fish. Not sure about your 'feel' for fish, i.e. getting potentially tricky fish to eat. But what about a medium tang as the centerpiece fish? A purple tang or Atlantic Blue Tang (<--- very underrated)?
