Aside from what others have already said, have you done a market study?
The most viable magic merchants today, especially on line, are specialty focused businesses; companies like Elusionist, Theory 11, and Paper Crane tend to focus on the under 25 crowd that's mainly interested in street styled performance as well as card art collectors. Then you have those that specialize in Bizarre styled paraphernalia like Lebanon Circle, Outlaw Effects, etc. The general all purpose trick shops are still out there, but their operators are in very tight competition with one another and too, you have to have big money to get started as well as to maintain such a venture.
You also need to understand that you will not be putting money into your own pocket for a minimum of two years when starting a business and yes, this is the norm when it comes to the typical business plan. Contrary to popular belief, owning a business does not mean you will have lots of free cash on hand. Of the many businesses I've been a founding member to, there have always been those situations in which the partners couldn't afford to buy, at cost, the items being sold. . . I helped in the design and development of Shadow Vision for an example but I certainly couldn't afford to build one for my own use; it cost us thousands of dollars (over $12,000.00) just to create the prototype. . . which brings me to the other reality point when it comes to doing magic retail. . .
If you're going to produce your own stuff, where will you build it? Do you have all the skills or resources for doing so? Have you considered R&D, Insurance, shop equipment costs, rent, etc. (you will need a physical facility for building these items).
Even if you are dealing with simple, commercial items and drop shipping everything YOU ARE RESPONSIBLE for getting the product out and to the buyer. If your supplier screws up an order they aren't the one's the patron will blame, YOU ARE! You will be responsible for returning the purchase price and shipping fees to the client if you can't fulfill the purchase agreement.
I'd recommend you put a good year or two into taking some small business courses including bookkeeping and marketing with a strong focus on internet merchandising. You may likewise wish to avail yourself with a very simplified overview about such work buy purchasing a copy of Richard Webster's "
Plan for Success".