Well you know what they say; the fastest way to end up with a million in the gun business is to start with two million.
For a moment, stop and think about your monthly overhead costs - rent (or mortgage & contruction costs), all the necessary business licenses, fees, utilities, insurance, etc. Add in how much profit you need to take out each month just to survive and pay all your personal bills. Add in the costs of personal and business taxes. Add in at least 10-15% of that total for contingencies and other costs I've probably forgetten to mention.
How many guns do you reasonably expect to sell in a month? Break it down by days. At how high a markup per unit?
Basically you need to write yourself out a business plan. An HONEST business plan that takes an unbiased view of how you will likely perform, not one that makes wild and unattainable projections based entirely upon how much you think you can do. Do some market research. Unless you've got a lot of capital to start with and can afford to live without income from the business for a good while, you're probably going to end up being the same type of store you're complaining about.
And sure, I know there's probably a lot of 'wealthy' people in that area, but that does not always translate into lots of sales. For example, I have no qualms about spending $5k-10k or more on a gun I like, but I don't buy too many guns (ie. low volume). When I do buy something, I find the deal I like and pay my FFL $50 or so to do a transfer. If you think people with money are spendthrifts, you've got another thing coming.
I'm not trying to dissuade you and I do wish you the best, but I had an FFL and its not as easy as you may think. Charge someone $30 over your cost and they'll still be whining about how you overcharged. Have at least one of every model for display? That takes a HUGE amount of money (just stop and think about all the various models and makes) and its a sunk cost that will not turn over to improve your ROI one iota.