As a former 5 location small business owner (not card shops), it is tough to make enough money to survive. There are so many things to consider, business insurance, health insurance, security, rent, utilities, accounting, taxes, inventory, pricing to stay competitive, payroll and more taxes, advertising, signage blah blah blah!
Before all that you'll need a business plan and some capital. Try going to a bank and asking for money to buy baseball or Pokémon cards. The banker will say, "Bless yer heart"!
I wouldn't rush into anything. Try online sales, like eBay. Get a table at a card show. Also, you better have another source of income for at the very least 2 years. If you do overcome the odds and make some money, don't spend it! You never know what is going to happen. And don't expect any days off or vacations for awhile.
On the other hand... nothing beats not working for the man!