I have done it and its pretty much a safe and easy trip. We always take several boats and booze cruise the day away with friends No wake zones will slow you down but if you put in at the Wapoo and go straight down an hour and a half at max.
And go under the Dawhoo and go the south Edisto to big bay creek or where ever you need to go.
I have been from Charleston to Beaufort and thats a good trip.
For trips like this I like to use the intracoastal strip charts. You would use 'Intracoastal Waterway Casino Creek to Beafort River'. Even if you have a chart plotter the paper charts are great so you can look at the trip in advance and refer to it a few minutes ahead while your running. When you get to the Edisto River you will continue down and leave the intracoastal for a few miles before getting to Edisto Beach. Watch the inlet to Big Bay Creek. Stay to the right until you past the Red "4" then cut straight in. There is a nice little waterfront along that back side of Edisto Beach. That should be a fun trip!!!