In my opinion you would never make a "killing" in this type of business. Doing an online store would certainly save you the trouble of having to lease a store front and all that entails.
I seriously considered several years ago what it would take for me to open a firearms retail store in my local community. I chose firearms because it's a passion. I quickly realized though that most passions are hard to turn into profitable businesses. After working on the initial research and business planning, I decided to abandon the idea and look for something else that's more lucrative.
All that said, here's my recommendation:
Write a business plan and formulate your anticipated expenses in a proforma-type spreadsheet, this way you can break-down things like expenses, cost of sales, net profits, gross profits, growth, etc. I may have an Excel sheet somewhere in my archive that you can use (all formulas keyed-in and ready for inputs). Let me know if you're interested.
Once you get that done, you'll have an idea of what the potential of the business would be. Take your time with it and expect writing the business plan, filling-out the proforma, and doing all the research to take months, not weeks.
Considering what type of business (ie: LLC, LP, SP, DBA, INC, etc.) is something you would want to research and potentially discuss with your tax adviser or CPA.
You'll also want to decide how you're going to fund the business initially. Are you going to the bank for a business loan? Are you using private funds? Are you going to have a partner? All this will be important and have implications on your bottom-line at the end of the day.
You may know all this already so apologies if I'm coming off too much like a big brother.