It is actually not a bad idea, it does not have to be Florida but a bigger state. Callifornia would not work since it is so left leaning and not a good representation of the US. Texas, Florida, New York or one of the bigger states in the rust belt would work much better.
The problem is Iowa does not tell you shit. The spend 100's of millions for roughly 100,000 people to show up and vote.
How about just doing away with the whole charade? Give everyone who wants to run one hour a week on PBS to state their case. Have Factcheck or some similar group verify all claims before they air. Have an open primary 6 months before the election, narrow the field down to four or so, then hold the election. Winner of the popular vote is prez, second place is VP.