Having gone pretty deep on this stuff in the last year or two thanks to my kids approaching college age, I'll pass along a few nuggets.
529s are a lot more flexible than they used to be. You can use them for certain K-12 expenses now, private school tuition, etc. You can change the beneficiary so if you oversave for one kid and undersave for the other, or you end up with extra and want to save it for a future grandchild, you can. You can also covert to a Roth, but there are lots of stipulations attached - including that the account has to be 15 years old. Do your homework.
You get no federal tax break for 529 contributions themselves, but you do get tax-free growth. In Iowa you get the state tax deduction, up to $6,100 per kid per year (or $12,200 if both parents have a 529 for that kid). You can still contribute to the 529 beyond $6,100/year, but $6,100 is the limit per account you can deduct.
When my kids were young I created a spreadsheet to figure out how the hell I would pay for college. The benchmark I used in my planning was "4 years at an in-state school" so I just took the cost of tuition, room and board, books, etc. at ISU and then increased it by the HEPI (Higher Education Price Index) each year until they were college age. The good news is, the actual cost of ISU now is significantly less than my projections were back then. Hopefully that holds true for all you with younger kids.
For anyone benchmarking against a Regents institution in Iowa, make sure you account for differential tuition. Students in certain majors (business, engineering, a few others) pay significantly higher tuition rates than the "base" rate starting in their sophomore years. If your student transfers in a lot of credits via AP or concurrent enrollment and starts their first year at ISU as a sophomore, that higher tuition rate won't start until their second year.