If you're starting at the airport, it's not reasonable to get to Venice in one day. You'll slow down to navigate through NO, then wait for a ferry to cross the river to Gretna. From there, the ride is a no-brainer on the shoulder of route 23. Take 2 days and meet some people to understand the area. You'll see levees on both sides keeping the Mississippi and Gulf out, learn about Katrina and BP. Dull ride, interesting story.