There are at least a couple major problems with this method. First, it's pretty easy to overlook quite a few expenses. Things like that daily stop at the coffee shop, or the cost of a car registration that happens only once a year.
If you are also planning to open your own business, you will definitely need some money as capital. And as far as the needed capital is needed, you should apply for a certain loan from a lender or bank. Such institutions will be more than happy in paying more depending on the ability that you have and they will surely be interested in knowing how you are actually managing your finances. When you can prove them that you are good in managing your finances, you will definitely get an approved application.