Remember the proverbial expression 'not seeing the wood for the trees'? You need to see the 'wood' first, then delve in and start examining the individual 'trees', meaning the individual items which you will be breaking down later. So a great point is to make sure that you have that overarching vision _ and if you cannot find one, then maybe it is an indication that you are obsessing on a few technical aspects that do not necessarily make up a whole business as you had imagined it. A business that makes sense and is going to be sustainable in the future is one that has that clear vision within which all the smaller parts contribute to make it successful.
As an example, let's say your current average number of transactions per month per customer is 3ǌ. Which says on average each customer does business with you 3 times each month. You could calculate how much more profit you would get if you could increase it to 3Ǒ. And I can tell you that would probably be enough to meet your plan. And if that did generate enough profit, all you would have to do is maintain everything else; sales, expenses, labor, average dollar sale, etc, and then just figure out how you could increase your transactions from 3ǌ to 3Ǒ. Maybe it could be with some type of promotion that would get customers to come in more often.