Henrik -
Not sure where you are from or your experience level.
".nu" indicates you are from Niue in Polynesia or, perhaps, New Zealand.
The usual cycling season for Iowa is about 6 months from mid-April to mid-October.
April & May can be cool and quite rainy - with big storms. Remember Dorothy in neighboring Kansas?
September & October can be delightful, getting chillier at night in October, but dry and crisp.
Mid-summer is usually pretty hot and humid, seriously sweaty cycling. But that's when most people ride.
Despite what people might think, Iowa is not flat.
The southern half of the state is hillier than the north.
The western third of the state has roller-coaster hills, one after another.
And there are steep bluffs along the Mississippi River.
Nearly every county has nice, county parks with not very many campers.
Type in the county name + "conservation". For ex. - "Poweshiek County Conservation".
You will be surprised how many options there are. Plus there are numerous state parks.
Winds are usually southerly in the summer, so either direction is fine.
I usually ride west to east, but I have gone both ways.
The Missouri River doesn't offer as many scenic points as the Mississippi.
There are a number of rail trails - mostly county operated - so they don't interconnect.
Also, most counties have lower traffic county roads - paved & unpaved.
I would avoid most state and US highways. Iowa highways generally do not have shoulders.
There is a state cycling map -
https://iowadot.gov/maps/msp/pdf/bikemap.pdfI really like to end my trip across Iowa in Davenport/Rock Island
because of the Riverside Trail right along the Mississippi RIver.
But there are so many options. Have fun!
Pic - Riverside Trail with Centennial Bridge, Davenport, Iowa