I'm going to have to agree with Pacu Mom. The turnover rate of fish is not good. That is why there are very few 'exotic' fish stores up and running. It is expensive to order a dozen EBJD's, and lose 4 in transit, and 3 to the new environment. Same with discus etc. I love the idea, but I've always heard mixing business with pleasure isn't a great idea.
I have often wondered though if a combination of stores were made... Say some type of food place... This would bring more customers in, and would help with advertising. Word of mouth is the quickest they say. You could have half the store setup to sell fish etc. and other products, and in the middle you could setup your display tanks so that people could eat, and enjoy the aros or pacus, or discus, or whatever. Maybe just make a wall between the two stores a couple of in-wall tanks? I don't know. Crazy idea, but IMO you need all the help you can get if you want to be successful selling fish.
I admire your heart, and I hope if you do infact decide to go through with it, that it does work out.
Matt.