I was visiting Sarasota to visit family for Thanksgiving and was told about the Legacy Trail so I decided to run it north to south. I could not find anything online or on Strava to show that anyone has run the full length before. Note that Google AI and the Friends of the Legacy website state the trail is 18.5 miles, but the printable map and signage at the south end extends a full 22.5 miles, so I kept going until I saw the final Legacy Trail sign at the south end. Except for a bit at the ends, the middle 15-18 miles are very straight and almost totally flat with elevation changes only for 3-4 road overpasses. The scenery is mostly backyards, woods, and marshes which are pleasant relative to the busy local roads.
There are many residential road crossings and crossings of several commercial streets where you could detour for water or food if necessary, but I just carried several bottles of gatorade, coke, water and some snacks and didn't make any stops to save the extra time roaming around.