The figure the court settled on in my divorce and custody case was based solely on AXH's then-last paystub - because that's the only info he provided - and that grudgingly. It also required that he reimburse me for 1/2 of the uncovered medical/dental expenses for DS. It didn't take into consideration daycare costs or tuition for the Waldorf school DS was in. Friends who have divorced (somewhat) amicably have that figure and then a share of the daycare or tuition costs as well as costs for extra-curricular activities (band, sports, etc). I believe they also lined out stipulations on college tuition and expenses for when the kids get older. I think it depends on the state and it depends on how the divorcing couple came up with the figures.
It'd probably help a great deal to line out the costs related to taking care of and raising your kids. Daycare expenses, what it costs to cover them under your medical insurance, costs if they play a musical instrument (lessons, equipment, etc.), the related fees if they're into school sports (gear, school fees, etc), even food and rent/housing. Having that info in hand would help determine if the minimum state requirement for support would be fair to all parties or if additional considerations would be helpful and agreeable to both parties. I think it'd be helpful for both the mediation and if you were to meet with a lawyer.