How do you become a millionaire farmer? Start out a multi-millionaire...
In all seriousness, though, starting out row-crop corn/sobyean farming from scratch is a pretty tough path--primarily due to the capital requirements for equipment/inputs as well as limited access to land. The nature of the business of growing commodities is that the low-cost producer wins, which can have as much to do with controlling your costs as growing the highest yields. Most of the successful smaller farmers I do not run the new equipment, and generally do as much as they can themselves rather than hiring things done (i.e. shopping around for inputs, spraying your own instead of having the coop spray name-brand herbicide, turning wrenches keeping equipment maintained, hauling own grain instead of hiring trucking, etc). Like any business there are different models that can make money, but for a smaller commodity operation you need to try to get as many dollars from what you have into your pocket and not someone else's... and even then may be difficult to generate an income that justifies the work required and amount of money you're putting at risk.
If starting an ag operation from scratch, I would definitely look to do something in the non-commodity space. I think there is opportunity to grow things and sell direct to end-user, which may be more labor-intensive but can make much more on a per-acre basis and give you much better control of the prices you're selling what you grow (vs being completely at the mercy of commodity markets).
ISU extension (and other ag-state extensions) have resources with budgets for different farm enterprises, equipment rental/custom rates, etc and also the Beginning Farmer Center. I believe Practical Farmers of Iowa also has some good information and networking opportunities with other people doing niche agriculture of all types.
There are some programs for beginning farmers; Iowa has a state income tax credit available for landlords who rent to beginning farmers (though qualification is mainly based on farmer net worth, which really makes it more of a "poor farmer tax credit"). There are some administrative fees waived on crop insurance, I think for your first 5 years. And some special programs for borrowing to make land purchases, though as some earlier eluded to I think they have quite a few hoops and may not be available to someone starting from scratch (one I looked at I think you had to have farmed for 3 years to qualify?).