Welcome to Fishlore (I know this isn't your first post, but I don't think I've said "hi" to you)
As for what to do with that 180g, you can just drop it off at my house (I live in MN, so it shouldn't be difficult). You don't really want anything that big, do you? I'll take good care of it for you.
Okay, seriously, now.
It looks like you've taken a shine to a number of South American fish. All three cichlids you mentioned, as well as the ghost knife, are from South America. It seems like they appreciate similar water qualities, which will help. I do not know a lot about cichlids, but I know that they can be aggressive, particularly when breeding. You could do a community tank, but I would suggest providing plenty of hiding places (the knife will need those, anyway). Lots of plants and driftwood can help break up sight lines. Some aquarists have had luck with larger tetras and cichlids. The tetras are fast and small enough to dive into smaller hiding places if attacked. The skirted tetras might work well for this. They're generally pretty uppity themselves, so they might do better with the stress of other aggressive fish.