So are you freshwater fish only or also saltwater, or even saltwater/reef? In my experience the freshwater fish crowd will not travel very far since they can feasibly get decent freshwater fish most anywhere, so it might be tougher to set yourself apart in that market. Saltwater fish are a bit more niche-friendly and if you get a good rep as a knowledgeable shop, people will travel for your services. Now, the ultimate niche is the saltwater-reef market, and as a reef aquarist, I can tell you that people like myself regularly travel 3+ hours to visit the best retail locations (vivid aquariums CA, world wide corals FL, Manhattan Reefs NY, Greenwich Aquaria CT as some examples).
It looks like you have a great start, a lot of great knowledge, and a busy location which is fantastic.
If you have any prior expertise in the reef side of things, I would urge you to dedicate even one small fish area to a display tank (where you can have all of your showpieces, things typically are not sold from this tank, it is a marketing investment), and several smaller tanks for coral or fish. The reason I am suggesting it is that having spent quite a bit of time in fish retail establishments, a big sale for freshwater fish is ~$100 in fish, but with saltwater, an average single fish may command that price and with coral, well, it just gets absurd how much things go for. Even the equipment is much more expensive. It just makes good business sense to carry some products which have super high profit margins.
Anyhow, I just wanted to write to say good luck and offer my humble opinions, I hope either way that you are successful and that your hard work is rewarded!
oh, last suggestion, I've been in a lot of fish stores. The typical owner/operator is a total shut-in very awkward, sarcastic, kind of like the comic book guy on the simpsons. If you are somewhat outgoing, polite, offer advise and info in a non-condescending way, and ensure that your employees do the same, you will immediately set yourself apart in this market. Godspeed!