SW Tank is going to get VERY expensive for 180gal. You will definitely have a comma in your budget for that. Plus it takes a lot more work to get it established. But with right equipment and a cycled tank, a tank that big won't require water changes as often, especially if you have 1.5-2 pounds per gallon of
live rock.
As for Fresh Water, your possibilities are almost limitless for cichlids. Again, you should invest in a
canister filter, as well as hang on filters. Any type of tank is fine for cichlids, but typically a rectangular tank is best because many cichlids are territorial, so having a long area to swim in would decrease any chance of fighting between fish, if you decide to go with aggressive cichlids.
If you like big fish an 180 gal would be fine for that, if you don't mind doing water changes and have good filtration, you could have 4 Oscars (in my opinion, other members might disagree).
Other bigger fish:
Jack Dempsey
Flowerhorn
Green Terror
hmmm...?
Or you could do a rad community cichlid tank with smaller cichlids, but don't mix african cichlids and american cichlids. Fishlore has some info on the difference.
Hope that helps. I am sure others will respond, I am still learning a lot too.