I have a little expierience with this. I have 3-125 gallon tanks,2-60 gallon vats,a 180 thats cycled but waiting for equipment,and a 4 foot clarity plus cube system running. They fill up extremely fast. Especially when people hear what your doing. I aquired most of my livestock through trades locally and over the internet. I have another 125 and a bank of 6 20 long tanks to get set up in the near future. I have so many different frags right now I have them almost stacked on top of each other.
As far as profit from this!!! Its going to take a long time to get the money out if it. I stopped counting at $15,000 and my wife says we are way beyond that (closing in on $25,000 and she does the books). So many times I thought about throwing in and cutting my losses. Niether of us anticipated it costing this much. I have had to sell off just about all my toys and give up alot of my hobbies for this. But, on the first day I was open it just seemed to be all worth it. Just the way the faces of the people looked when they saw what I have built from nothing to reality.
The money to me really is secondary. The store intentionally was to only be a coral farm but my employer is cutting jobs left and right and I am so low on the totem pole that it is inevitable that my job will be cut in about 18-36 months. Hopefully in the next two to three years I can start to turn a good profit from it. I can not see it being a sole source of income for my family. But it can be a good source of income.
You can't discount the local sales. Depending on where you live that can be the bulk of your sales. I thought the same thing as you. And my wife is increasingly paranoid about the situation. I got a BIG,BIG rotweiler puppy and am so surprised at how protective he can be with the family. Set your website up to allow people to pick up orders locally at your doorstep or send/deliver them via taxi/yourself. Charge a lesser fee. Honestly people will laugh and say it won't work but when they can save $20-$50 on a $150 order over going to a walk up pet store they will expect to jump through a few hoops. The fact that they can go directly to your website and see exactly what you have to offer may mean they don't even have to leave the house. You do lose the impulse sale to an extent this way. I respect the fact that most customers will want to see what conditions my corals are grown in and have no problem showing them as long as they set up an order or show an interest in a specific coral. You do have to earn the customers trust. But after you do they will respect your conditions of sale.
Sorry if I got off base a little,but there are more things to worry about than just profit IMO.
gooch