The first big question: Are you happy with it as it looks today? If so, keeping it going as-is shouldn't be hard. If not, what are your goals? Are you trying to turn it in to a more colorful reef, different fish, or something else?A picture of the back (and the front for that matter) would help. I'm having a hard time telling from the description if it's an older all in one (I've seen a few in that size range), or if you are saying the filtration is in a separate container behind the main display. Depending on your goals, you can almost certainly keep it going or do something nice with the current system. You could replace it, but it will probably be much cheaper not to, and almost anything can be worked around with the right skill set.The lowest cost option is to read, ask questions here, and visit other members. At least most of the people I know are happy to explain what they are doing to anyone who wants to come by when they are maintaining their tanks. IMO most people with enough time reading then asking questions as needed can maintain their own reefs. Some do better than others, but as with anything else, it gets easier with experience. Alternatively, if you want to hire someone to do some training, there are plenty of options for that as well.There isn't anything in that fish list that is terribly sensitive, so I'd say there's not immediate peril as you get things figured out. Just be careful not to stab yourself on the long spine urchin. The maroons and damsels can be rather, ahem, assertive, so take care in selecting future fish if you keep those.A lot of built in systems don't think out ventilation very well. If you're having a mold issue, glass lids if there aren't any, and a 5v or 12v fan to vent the air above the aquarium will go a long way to preventing recurrence once you get it cleaned up a bit. If you're not and the drywall just looks poorly finished or like it has been hit in places, that isn't unusual behind built ins either as few people ever see it.Finally, please post a location! Zip code is fine, we don't need your exact address, but even if you're out in the middle of nowhere it might turn out that an experienced member lives right around the corner from you. This happens more often than you might think.