Hear my tale. Early on in keeping fish I got the idea that the best way to have more fish might be to own a fish store. I began to do the research on what that would take in terms of time and money. My goal was really simple. I did not care if the store never made me a profit. However, I needed to be certain going in that I could be 100% sure I would also not lose my shirt.
I crunched numbers and looked at all the options and I never opened a store. So instead of looking at all the benefits, consider the potential downsides. You have to stock your store. Unless you are pretty wealthy this means you will have to select what you stock. Decide wrong and you are stuck with fish you cannot sell and have to feed etc. Or you get in a nice shipment of fish which included some disease and the entire shipment dies. So one of the most important skills you will need is in diagnosing and treating fish.
I have known a few folks who have started stores, almost none managed to make it work for more than a few years. So my advice is to start home based. Most of your sales will be shipped. I allow people to come to my home to buy fish by appointment, but you may not want to do this. Consider how many people there are in Iowa who keep fish and might travel to you. Then consider how many fish keepers their are in America. Finally, consider what fish you can offer that are not cheap and easy to find.
Also, I began with my first expensive plecos in 2006. At the same time we were caring for my mother, who had dementia, at home. It quickly became obvious that I had a tank full of zebra pleco babies and a mother who could not deal with an extended loss of electricity. So we installed a whole house back-up generator. Before it was hooked up, we had a power outage. To keep my fish alive and safe I used battery powered air pumps rotated between tanks. But I needed to keep the zebras warm. So I was removing tank water to a pot and then heating it on the outdoor grill and putting back into the tank. At that time I estimated I had $15k worth of zebras plus my other fish not to mention the value of mom.
If you are serious about this project, you need to be sure you have covered all the bases. In 2011 and 2012 we had big hurricanes which came up the east coast and through NY. Both times the power from the utility was out for 13 days. The generator turned out to be one the best money we have ever spent.
Finally, seek out folks who have done what you are wanting to do and pump them for any info you can. Over the years I have purchased many 100s of fish, maybe 1,000s. I have spawned some, I have bought wholesale and I have bought imports. I have managed to make my hobby pay for itself. But I also started later in life and so money was less of a problem the longer I was keeping fish. But there were still some big risks involved. I paid many $1,000s for each of the last two groups of fish I purchased. I worked my way up to this over more than a decade and I did not begin this course until I was 5+ years into the hobby.
The best advice I can offer here is start slow. Then use each success to build things a bit bigger. And do not make the most common mistake most new business owners do. We all underestimate how much time and money will be needed to get it all started. I never had more than 28 tanks going at one time including my display tanks.
Lastly, take pride in what you do. The only way to succeed longer term at this is to be selling a quality product. Like I often tell folks, "One healthy fish has to worth at least 3 DOAS."
Good luck and be sure to have fun doing it. That is half the point of it all.
edited for typos