You're operating under some misconceptions, OP. For starters, OH uses an income share model for calculation of child support. That means that the income of both parents is used in calculating the support obligation. How that works is the total combined income is used to calculate the support obligation (and I'm not sure what the percentages are for 3 kids). Then that figure is split proportionally. So, if one parent is making $40k and the other is making $20k, the parent with the higher income is responsible for 2/3's of the support - whether that is the CP or the NCP, male or female. So, supposing the support figure is $1200/mo and the CP makes the higher income. The NCP would still be required to pay $400/mo. There are other factors that typically factor into the calculation - amount of time with the NCP, for example.
OH does also provide a credit for childcare needs, insurance premiums, and support obligations for other bio children (outgoing OR incoming).
Personally, considering that the children have been with you for nearly a year, the likelihood of a judge changing custody is low. Judges don't like to disrupt an existing living arrangement unless there is a good reason (the kids are being abused, neglected, etc). However, noone can guarantee that it won't happen. Only you can decide (preferably with the advice of an attorney who knows all of the facts) what your best course of action might be.