Can you walk around without paying admission, or do you need to pay just to even get onto the site?

You have to pay upon entry. Parking is free.

You can walk around the grounds without paying admission. No parking fees also.

You can drive to the parking area and shop for garden shrubs without entering the actual garden.

Admission to the gardens is $29. You have to pay upon entry. We didn't see anyway to walk around for free. The house tours, etc are extra.

Yes, you can walk around the plantation without paying. But the jitney tour tells you what you're looking at and explains the history. You would also have to avoid Bubba, the 10 ft alligator who sometimes suns himself in the middle of the road. The house tour is a separate admission.