Don't quit your day job.
The math is pretty basic.
There are 52 weeks in a year. Retail photography is somewhat seasonal, so figure you will only shoot about 46-48 weeks a year.
We'll use 48 weeks. You might get lucky and squeeze in a couple more weeks, but don't count on it and consider any extra you can squeeze in as gravy.
Most of the time devoted a successful retail photography business goes to business tasks. Doing the accounting, planning promotions, pay bills, tweaking your marketing plan, preparing your quarterly tax payments, making sure you're forwarding the state sales taxes, paying use tax, generating new customers, getting previous customers back again, networking with other businesses, on going education, attending workshops/industry conventions, etc.
So, it turns out that out of a 7 day week, and assuming you only take 1 day off a week you can only plan on 3 shooting days. The other 4 days go to editing, customer contact, delivering your product to the client, getting the oil changed in the car, grocery shopping, getting a hair cut, yada, yada, yada.
So - 48 weeks time 3 shooting days a week = 144 shooting days.
Lets figure 3 shoots per shooting day, but 2 per shooting day is more realistic, particularly if you don't have a studio.
Ok- so 3 shoot per shooting day time 144 shooting days = 432 shoots (sales) per year. Or put another way, you'll have to come up with 432 clients in a year.
If your gross income is 20% of your total revenue, and your gross salary is $30,000 a year - you need yearly revenue of $150,000 per year.
20% x 150,000 = $30,000
On average that is $12,500 per month, or average revenue of $2907 per week.
By the way. If your gross income is $30,000 a year about $7000 a year will go to state and federal income taxes, FICA, etc and you will need to live on about $23,000.
So, $150,000 a year divided by 432 shoots per year means you'll need an average sale per shoot of just about $350.
How much were you planning to charge, flat rate, for a 1 hour shoot that includes a CD of edited images?
Oh, customers take forever to choose from images that are online, because it's too easy to look at them that way. Proofing in person works much better.
From a 1 hour session I would not show the client more than 20 - 25 images. Other wise they have to many choices and again, take forever to decide.