Choclate I will repeat again and again and again and AGAIN in my area there is NO petsmart and NO petco.
Currently it is more online anyways, then hopefully leading up to a store front as well. I wanted to do a pet store initially (and then was amazed at how many people shot me down... Maybe because they fear failure?) since certain things are pretty easy to make (dog clothes are a high seller for example). But for now work on fish, then reptiles - since my area loves reptiles as well, then other animals... Working in coordination with shelters of course.
Once there is a store front and you branch out... Since there is not Petsmart/Co in your area -- I like how they work with animal shelters. The shelters bring in adoptable dogs/cats for an Adoption Day -- and the store sells accompanying items (foods, bowls, beds, etc.) I can definitely see your store filling this niche, since there isn't a Petsmart/Co doing this in the area. As you've mentioned, supplies/equipment is a good money maker, and you won't have to worry (much) about shelf-life or climate control.
As for people shooting you down, that's their problem, not yours. If it's your dream and your desire, you should think out as many aspects as you can (which is what you're doing) and then if it's still your dream and desire - go for it.
I think that a big part of being successful is a) determining how to reach potential customers, and then b) turning them into repeat customers (who also bring their friends in).
What about 'activities?' Think Home Depot/Lowes - they have "How To" sessions. You could do a "how to create a planted tank" class. It could be free (like Lowes/Home Depot), and then people could buy the tanks/plants from you. Or you could charge a fee to cover the costs of materials, and people could set things up during the session. Etc.
Also, with regard to activities, think about socialization. People who come in, do things, and make friends in the process -- will probably come back again.
etc etc etc...........