The weekends are NUTS out there. It is a full no go. The lines are literally over a mile long to get in the main Dunes state park. Central beach is closed due to erosion, and Mt Baldy also gets crazy on weekends.
Monday through Friday afternoon is great though. I love it. I can give you some trail recommendations even based on how much walking and hiking you want to do, and how tough you want it to be. There are some other lesser known area of the National Park and trails that are kind of off of the beaten path that aren't even really busy on the weekends though, which is usually where we go. The Bailley Homestead/Chellberg Farm area has a nice section of the Calumet Trail that is 3.5 to 4 miles in the woods with a bit of up and down, and most of it is EMPTY, even on a weekend.